magnum/src/Magnum/Text/Renderer.cpp

/*
    This file is part of Magnum.

    Copyright © 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019,
                2020, 2021, 2022, 2023, 2024, 2025
              Vladimír Vondruš <mosra@centrum.cz>

    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the "Software"),
    to deal in the Software without restriction, including without limitation
    the rights to use, copy, modify, merge, publish, distribute, sublicense,
    and/or sell copies of the Software, and to permit persons to whom the
    Software is furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included
    in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
    DEALINGS IN THE SOFTWARE.
*/

#include "Renderer.h"

#include <Corrade/Containers/StridedArrayView.h>
#include <Corrade/Containers/Optional.h>
#include <Corrade/Containers/Triple.h>

#include "Magnum/Math/Functions.h"
#include "Magnum/Math/Range.h"
#include "Magnum/Text/AbstractFont.h"
#include "Magnum/Text/AbstractGlyphCache.h"
#include "Magnum/Text/Alignment.h"
#include "Magnum/Text/Direction.h"

#ifdef MAGNUM_TARGET_GL
#include <Corrade/Containers/Array.h>
#include <Corrade/Containers/ArrayViewStl.h> /** @todo remove once Renderer is STL-free */
#include <Corrade/Containers/StringStl.h> /** @todo remove once Renderer is STL-free */

#include "Magnum/Mesh.h"
#include "Magnum/GL/Context.h"
#include "Magnum/GL/Extensions.h"
#include "Magnum/GL/Mesh.h"
#include "Magnum/Shaders/GenericGL.h"
#include "Magnum/Text/AbstractShaper.h"
#endif

namespace Magnum { namespace Text {

Range2D renderLineGlyphPositionsInto(const AbstractFont& font, const Float size, const LayoutDirection direction, const Containers::StridedArrayView1D<const Vector2>& glyphOffsets, const Containers::StridedArrayView1D<const Vector2>& glyphAdvances, Vector2& cursor, const Containers::StridedArrayView1D<Vector2>& glyphPositions) {
    CORRADE_ASSERT(glyphAdvances.size() == glyphOffsets.size() &&
                   glyphPositions.size() == glyphOffsets.size(),
        "Text::renderLineGlyphPositionsInto(): expected glyphOffsets, glyphAdvances and output views to have the same size, got" << glyphOffsets.size() << Debug::nospace << "," << glyphAdvances.size() << "and" << glyphPositions.size(), {});
    CORRADE_ASSERT(direction == LayoutDirection::HorizontalTopToBottom,
        "Text::renderLineGlyphPositionsInto(): only" << LayoutDirection::HorizontalTopToBottom << "is supported right now, got" << direction, {});
    #ifdef CORRADE_NO_ASSERT
    static_cast<void>(direction); /** @todo drop once implemented */
    #endif

    CORRADE_ASSERT(font.isOpened(),
        "Text::renderLineGlyphPositionsInto(): no font opened", {});
    const Float scale = size/font.size();

    /* Combine the offsets and cursor advances and calculate the line rectangle
       along the way. Initially the cursor is at origin and rectangle is empty,
       with just the Y bounds from font metrics. */
    /** @todo this needs an update for vertical text */
    Range2D rectangle{cursor + Vector2::yAxis(font.descent()*scale),
                      cursor + Vector2::yAxis(font.ascent()*scale)};
    for(UnsignedInt i = 0; i != glyphOffsets.size(); ++i) {
        /* The glyphOffsets and output are allowed to be aliased, so make sure
           the value isn't stomped on when writing the output */
        glyphPositions[i] = cursor + glyphOffsets[i]*scale;
        cursor += glyphAdvances[i]*scale;

        /* Extend the line rectangle with the cursor range */
        /** @todo this assumes left-to-right / top-to-bottom ordering of
            shaped glyphs (which HarfBuzz does for both directions however),
            add some checks to verify that assumption */
        rectangle.max() = Math::max(rectangle.max(), cursor);
    }

    return rectangle;
}

namespace {

Range2D renderGlyphQuadsInto(const AbstractGlyphCache& cache, const Float scale, const Containers::StridedArrayView1D<const Vector2>& glyphPositions, const Containers::StridedArrayView1D<const UnsignedInt>& glyphIds, const Containers::StridedArrayView1D<Vector2>& vertexPositions, const Containers::StridedArrayView1D<Vector2>& vertexTextureCoordinates, const Containers::StridedArrayView1D<Float>& vertexTextureLayers) {
    CORRADE_ASSERT(glyphIds.size() == glyphPositions.size(),
        "Text::renderGlyphQuadsInto(): expected glyphIds and glyphPositions views to have the same size, got" << glyphIds.size() << "and" << glyphPositions.size(), {});
    CORRADE_ASSERT(vertexPositions.size() == glyphPositions.size()*4 &&
                   vertexTextureCoordinates.size() == glyphPositions.size()*4,
        "Text::renderGlyphQuadsInto(): expected vertexPositions and vertexTextureCoordinates views to have" << glyphPositions.size()*4 << "elements, got" << vertexPositions.size() << "and" << vertexTextureCoordinates.size(), {});
    /* Should be ensured by the callers below */
    CORRADE_INTERNAL_ASSERT(!vertexTextureLayers || vertexTextureLayers.size() == vertexTextureCoordinates.size());

    /* Direct views on the cache data */
    const Vector2 inverseCacheSize = 1.0f/Vector2{cache.size().xy()};
    const Containers::StridedArrayView1D<const Vector2i> cacheGlyphOffsets = cache.glyphOffsets();
    const Containers::StridedArrayView1D<const Int> cacheGlyphLayers = cache.glyphLayers();
    const Containers::StridedArrayView1D<const Range2Di> cacheGlyphRectangles = cache.glyphRectangles();

    /* Create quads for each glyph and calculate the glyph bound rectangle
       along the way. */
    Range2D rectangle;
    for(std::size_t i = 0; i != glyphIds.size(); ++i) {
        /* 2---3
           |   |
           |   |
           |   |
           0---1 */
        const UnsignedInt glyphId = glyphIds[i];
        const Range2D quad = Range2D::fromSize(
            glyphPositions[i] + Vector2{cacheGlyphOffsets[glyphId]}*scale,
            Vector2{cacheGlyphRectangles[glyphId].size()}*scale);
        const Range2D texture = Range2D{cacheGlyphRectangles[glyphId]}
            .scaled(inverseCacheSize);
        const std::size_t i4 = i*4;
        for(UnsignedByte j = 0; j != 4; ++j) {
            /* ✨ */
            vertexPositions[i4 + j] = Math::lerp(quad.min(), quad.max(), BitVector2{j});
            vertexTextureCoordinates[i4 + j] = Math::lerp(texture.min(), texture.max(), BitVector2{j});
        }

        /* Fill also a texture layer if desirable. For 2D output the caller
           already checked that the cache is 2D. */
        if(vertexTextureLayers) for(std::size_t j = 0; j != 4; ++j)
            vertexTextureLayers[i4 + j] = cacheGlyphLayers[glyphId];

        /* Extend the rectangle with current glyph bounds */
        rectangle = Math::join(rectangle, quad);
    }

    return rectangle;
}

Range2D renderGlyphQuadsInto(const AbstractFont& font, const Float size, const AbstractGlyphCache& cache, const Containers::StridedArrayView1D<const Vector2>& glyphPositions, const Containers::StridedArrayView1D<const UnsignedInt>& fontGlyphIds, const Containers::StridedArrayView1D<Vector2>& vertexPositions, const Containers::StridedArrayView1D<Vector2>& vertexTextureCoordinates, const Containers::StridedArrayView1D<Float>& vertexTextureLayers) {
    CORRADE_ASSERT(font.isOpened(),
        "Text::renderGlyphQuadsInto(): no font opened", {});

    const Containers::Optional<UnsignedInt> fontId = cache.findFont(font);
    CORRADE_ASSERT(fontId,
        "Text::renderGlyphQuadsInto(): font not found among" << cache.fontCount() << "fonts in passed glyph cache", {});

    /* First map the font-local glyph IDs to cache-global, abusing the texture
       coordinate output array as the storage. Not vertex positions, as those
       are allowed to be aliased with glyphPositions by the caller and this
       process would overwrite them.

       This also means we need to duplicate the size assertions here, to avoid
       asserting inside glyphIdsInto() instead and confusing the user. */
    CORRADE_ASSERT(fontGlyphIds.size() == glyphPositions.size(),
        "Text::renderGlyphQuadsInto(): expected fontGlyphIds and glyphPositions views to have the same size, got" << fontGlyphIds.size() << "and" << glyphPositions.size(), {});
    CORRADE_ASSERT(vertexPositions.size() == glyphPositions.size()*4 &&
                   vertexTextureCoordinates.size() == glyphPositions.size()*4,
        "Text::renderGlyphQuadsInto(): expected vertexPositions and vertexTextureCoordinates views to have" << glyphPositions.size()*4 << "elements, got" << vertexPositions.size() << "and" << vertexTextureCoordinates.size(), {});
    const Containers::StridedArrayView1D<UnsignedInt> glyphIds = Containers::arrayCast<UnsignedInt>(vertexTextureCoordinates.every(4));
    cache.glyphIdsInto(*fontId, fontGlyphIds, glyphIds);

    /* Delegate to the above */
    return renderGlyphQuadsInto(cache, size/font.size(), glyphPositions, glyphIds, vertexPositions, vertexTextureCoordinates, vertexTextureLayers);
}

}

Range2D renderGlyphQuadsInto(const AbstractFont& font, const Float size, const AbstractGlyphCache& cache, const Containers::StridedArrayView1D<const Vector2>& glyphPositions, const Containers::StridedArrayView1D<const UnsignedInt>& glyphIds, const Containers::StridedArrayView1D<Vector2>& vertexPositions, const Containers::StridedArrayView1D<Vector3>& vertexTextureCoordinates) {
    return renderGlyphQuadsInto(font, size, cache, glyphPositions, glyphIds, vertexPositions, vertexTextureCoordinates.slice(&Vector3::xy), vertexTextureCoordinates.slice(&Vector3::z));
}

Range2D renderGlyphQuadsInto(const AbstractFont& font, const Float size, const AbstractGlyphCache& cache, const Containers::StridedArrayView1D<const Vector2>& glyphPositions, const Containers::StridedArrayView1D<const UnsignedInt>& glyphIds, const Containers::StridedArrayView1D<Vector2>& vertexPositions, const Containers::StridedArrayView1D<Vector2>& vertexTextureCoordinates) {
    CORRADE_ASSERT(cache.size().z() == 1,
        "Text::renderGlyphQuadsInto(): can't use this overload with an array glyph cache", {});
    return renderGlyphQuadsInto(font, size, cache, glyphPositions, glyphIds, vertexPositions, vertexTextureCoordinates, nullptr);
}

Range2D renderGlyphQuadsInto(const AbstractGlyphCache& cache, const Float scale, const Containers::StridedArrayView1D<const Vector2>& glyphPositions, const Containers::StridedArrayView1D<const UnsignedInt>& glyphIds, const Containers::StridedArrayView1D<Vector2>& vertexPositions, const Containers::StridedArrayView1D<Vector3>& vertexTextureCoordinates) {
    return renderGlyphQuadsInto(cache, scale, glyphPositions, glyphIds, vertexPositions, vertexTextureCoordinates.slice(&Vector3::xy), vertexTextureCoordinates.slice(&Vector3::z));
}

Range2D renderGlyphQuadsInto(const AbstractGlyphCache& cache, const Float scale, const Containers::StridedArrayView1D<const Vector2>& glyphPositions, const Containers::StridedArrayView1D<const UnsignedInt>& glyphIds, const Containers::StridedArrayView1D<Vector2>& vertexPositions, const Containers::StridedArrayView1D<Vector2>& vertexTextureCoordinates) {
    CORRADE_ASSERT(cache.size().z() == 1,
        "Text::renderGlyphQuadsInto(): can't use this overload with an array glyph cache", {});
    return renderGlyphQuadsInto(cache, scale, glyphPositions, glyphIds, vertexPositions, vertexTextureCoordinates, nullptr);
}

Range2D alignRenderedLine(const Range2D& lineRectangle, const LayoutDirection direction, const Alignment alignment, const Containers::StridedArrayView1D<Vector2>& positions) {
    CORRADE_ASSERT(direction == LayoutDirection::HorizontalTopToBottom,
        "Text::alignRenderedLine(): only" << LayoutDirection::HorizontalTopToBottom << "is supported right now, got" << direction, {});
    CORRADE_ASSERT(
        (UnsignedByte(alignment) & Implementation::AlignmentHorizontal) != Implementation::AlignmentStart &&
        (UnsignedByte(alignment) & Implementation::AlignmentHorizontal) != Implementation::AlignmentEnd,
        "Text::alignRenderedLine():" << alignment << "has to be resolved to *Left / *Right before being passed to this function", {});
    #ifdef CORRADE_NO_ASSERT
    static_cast<void>(direction); /** @todo drop once implemented */
    #endif

    /** @todo this again assumes horizontal direction, needs to be updated once
        vertical (and possibly mixed horizontal/vertical) text is possible */

    Float alignmentOffsetX;
    if((UnsignedByte(alignment) & Implementation::AlignmentHorizontal) == Implementation::AlignmentLeft)
        alignmentOffsetX = -lineRectangle.left();
    else if((UnsignedByte(alignment) & Implementation::AlignmentHorizontal) == Implementation::AlignmentCenter) {
        alignmentOffsetX = -lineRectangle.centerX();
        /* Integer alignment */
        if(UnsignedByte(alignment) & Implementation::AlignmentIntegral)
            alignmentOffsetX = Math::round(alignmentOffsetX);
    }
    else if((UnsignedByte(alignment) & Implementation::AlignmentHorizontal) == Implementation::AlignmentRight)
        alignmentOffsetX = -lineRectangle.right();
    else CORRADE_INTERNAL_ASSERT_UNREACHABLE(); /* LCOV_EXCL_LINE */

    /* Shift all positions */
    for(Vector2& i: positions)
        i.x() += alignmentOffsetX;

    return lineRectangle.translated(Vector2::xAxis(alignmentOffsetX));
}

Range2D alignRenderedBlock(const Range2D& blockRectangle, const LayoutDirection direction, const Alignment alignment, const Containers::StridedArrayView1D<Vector2>& positions) {
    CORRADE_ASSERT(direction == LayoutDirection::HorizontalTopToBottom,
        "Text::alignRenderedBlock(): only" << LayoutDirection::HorizontalTopToBottom << "is supported right now, got" << direction, {});
    CORRADE_ASSERT(
        (UnsignedByte(alignment) & Implementation::AlignmentHorizontal) != Implementation::AlignmentStart &&
        (UnsignedByte(alignment) & Implementation::AlignmentHorizontal) != Implementation::AlignmentEnd,
        "Text::alignRenderedBlock():" << alignment << "has to be resolved to *Left / *Right before being passed to this function", {});
    #ifdef CORRADE_NO_ASSERT
    static_cast<void>(direction); /** @todo drop once implemented */
    #endif

    /** @todo this assumes vertical layout advance, needs to be updated once
        other directions are possible */

    Float alignmentOffsetY;
    if((UnsignedByte(alignment) & Implementation::AlignmentVertical) == Implementation::AlignmentLine)
        alignmentOffsetY = 0.0f;
    else if((UnsignedByte(alignment) & Implementation::AlignmentVertical) == Implementation::AlignmentBottom)
        alignmentOffsetY = -blockRectangle.bottom();
    else if((UnsignedByte(alignment) & Implementation::AlignmentVertical) == Implementation::AlignmentMiddle) {
        alignmentOffsetY = -blockRectangle.centerY();
        /* Integer alignment */
        if(UnsignedByte(alignment) & Implementation::AlignmentIntegral)
            alignmentOffsetY = Math::round(alignmentOffsetY);
    }
    else if((UnsignedByte(alignment) & Implementation::AlignmentVertical) == Implementation::AlignmentTop)
        alignmentOffsetY = -blockRectangle.top();
    else CORRADE_INTERNAL_ASSERT_UNREACHABLE(); /* LCOV_EXCL_LINE */

    /* Shift all positions */
    for(Vector2& i: positions)
        i.y() += alignmentOffsetY;

    return blockRectangle.translated(Vector2::yAxis(alignmentOffsetY));
}

namespace {

template<class T> void renderGlyphQuadIndicesIntoInternal(const UnsignedInt glyphOffset, const Containers::StridedArrayView1D<T>& indices) {
    CORRADE_ASSERT(indices.size() % 6 == 0,
        "Text::renderGlyphQuadIndicesInto(): expected the indices view size to be divisible by 6, got" << indices.size(), );
    const UnsignedInt glyphCount = indices.size()/6;
    #ifndef CORRADE_NO_ASSERT
    const UnsignedLong maxValue = UnsignedLong(glyphOffset)*4 + UnsignedLong(glyphCount)*4;
    #endif
    CORRADE_ASSERT(maxValue <= (1ull << 8*sizeof(T)),
        "Text::renderGlyphQuadIndicesInto(): max index value of" << maxValue - 1 << "cannot fit into a" << 8*sizeof(T) << Debug::nospace << "-bit type", );

    for(UnsignedInt i = 0; i != glyphCount; ++i) {
        /* 2---3 2 3---5
           |   | |\ \  |
           |   | | \ \ |
           |   | |  \ \|
           0---1 0---1 4 */
        const UnsignedInt i4 = (glyphOffset + i)*4;
        const UnsignedInt i6 = i*6;
        indices[i6 + 0] = i4 + 0;
        indices[i6 + 1] = i4 + 1;
        indices[i6 + 2] = i4 + 2;
        indices[i6 + 3] = i4 + 2;
        indices[i6 + 4] = i4 + 1;
        indices[i6 + 5] = i4 + 3;
    }
}

}

void renderGlyphQuadIndicesInto(UnsignedInt glyphOffset, const Containers::StridedArrayView1D<UnsignedInt>& indices) {
    renderGlyphQuadIndicesIntoInternal(glyphOffset, indices);
}

void renderGlyphQuadIndicesInto(UnsignedInt glyphOffset, const Containers::StridedArrayView1D<UnsignedShort>& indices) {
    renderGlyphQuadIndicesIntoInternal(glyphOffset, indices);
}

void renderGlyphQuadIndicesInto(UnsignedInt glyphOffset, const Containers::StridedArrayView1D<UnsignedByte>& indices) {
    renderGlyphQuadIndicesIntoInternal(glyphOffset, indices);
}

Containers::Pair<UnsignedInt, UnsignedInt> glyphRangeForBytes(const Containers::StridedArrayView1D<const UnsignedInt>& clusters, const UnsignedInt begin, const UnsignedInt end) {
    if(clusters.isEmpty())
        return {};

    /* Make the begin always less than or equal to end */
    const bool reverseBeginEnd = begin > end;
    const UnsignedInt beginForward = reverseBeginEnd ? end : begin;
    const UnsignedInt endForward = reverseBeginEnd ? begin : end;

    /* Make the cluster array always in an ascending order as well */
    const bool reverseClusters = clusters.front() > clusters.back();
    const Containers::StridedArrayView1D<const UnsignedInt> clustersForward =
        reverseClusters ? clusters.flipped<0>() : clusters;

    /* The glyph begin is the last glyph that has the cluster ID not larger
       than `begin`, or the end */
    UnsignedInt glyphBegin = 0;
    while(glyphBegin != clustersForward.size() && clustersForward[glyphBegin] < beginForward && (glyphBegin + 1 == clustersForward.size() || clustersForward[glyphBegin + 1] <= beginForward))
        ++glyphBegin;

    /* If `begin` was pointing in the middle of a cluster, for example of a
       ligature, or (wrongly) inside a multi-byte UTF-8 char, go back to find
       the cluster begin */
    if(glyphBegin != clustersForward.size()) while(glyphBegin && clustersForward[glyphBegin - 1] == clustersForward[glyphBegin])
        --glyphBegin;

    /* The end is then the first glyph after glyph begin that has the cluster
       ID larger or equal to `end`. Unless `begin` was the same as `end`, then
       the returned glyph end is same as returned glyph begin. */
    UnsignedInt glyphEnd = glyphBegin;
    if(beginForward != endForward) while(glyphEnd != clustersForward.size() && clustersForward[glyphEnd] < endForward)
        ++glyphEnd;

    /* If the clusters were in reverse direction, reverse the actual glyph IDs
       as well. And this way the begin is greater or equal to end, so they're
       swapped too. */
    const Containers::Pair<UnsignedInt, UnsignedInt> out = reverseClusters ?
        Containers::pair(UnsignedInt(clustersForward.size()) - glyphEnd,
                         UnsignedInt(clustersForward.size()) - glyphBegin) :
        Containers::pair(glyphBegin, glyphEnd);

    /* Then, if the begin and end was swapped, swap the output again as well */
    return reverseBeginEnd ?
        Containers::pair(out.second(), out.first()) :
        out;
}

#ifdef MAGNUM_TARGET_GL
namespace {

struct Vertex {
    Vector2 position, textureCoordinates;
};

std::tuple<std::vector<Vertex>, Range2D> renderVerticesInternal(AbstractFont& font, const AbstractGlyphCache& cache, const Float size, const std::string& text, const Alignment alignment) {
    /* This was originally added as a runtime error into plugin implementations
       during the transition period for the new AbstractGlyphCache API, now
       it's an assert in the transition period for the Renderer API. Shouldn't
       get triggered by existing code that uses 2D caches. */
    CORRADE_ASSERT(cache.size().z() == 1,
        "Text::Renderer: array glyph caches are not supported", {});

    /* Find this font in the cache and assert in the high-level API already to
       avoid confusion */
    CORRADE_ASSERT(cache.findFont(font),
        "Text::Renderer: font not found among" << cache.fontCount() << "fonts in passed glyph cache", {});

    /* Output data, reserve memory as when the text would be ASCII-only. In
       reality the actual vertex count will be smaller, but allocating more at
       once is better than reallocating many times later. */
    std::vector<Vertex> vertices;
    vertices.reserve(text.size()*4);

    /* Scaling factor, line advance, total rendered bounds, initial line
       position, last+1 vertex on previous line */
    const Float scale = size/font.size();
    const Vector2 lineAdvance = Vector2::yAxis(font.lineHeight()*scale);
    Range2D rectangle;
    Vector2 linePosition;

    /* Temp buffer so we don't allocate for each new line */
    std::string line;
    line.reserve(text.size());

    /* Create a shaper */
    /** @todo even with reusing a shaper this is all horrific, rework!! */
    Containers::Pointer<AbstractShaper> shaper = font.createShaper();

    /* Start/End alignment resolved based on what the shaper detects for the
       first line. Not great, but can't do much better with this old limited
       API. */
    /** @todo rework all this, again */
    Containers::Optional<Alignment> resolvedAlignment;

    /* Render each line separately and align it horizontally */
    std::size_t pos, prevPos = 0;
    do {
        /* Empty line, nothing to do (the rest is done below in while expression) */
        if((pos = text.find('\n', prevPos)) == prevPos) continue;

        /* Copy the line into the temp buffer */
        line.assign(text, prevPos, pos-prevPos);

        /* Shape the line */
        shaper->shape(line);

        /* Verify that we don't reallocate anything. The only problem might
           arise when the layouter decides to compose one character from more
           than one glyph (i.e. accents). Will remove the asserts when this
           issue arises. */
        CORRADE_INTERNAL_ASSERT(vertices.size() + shaper->glyphCount()*4 <= vertices.capacity());
        vertices.resize(vertices.size() + shaper->glyphCount()*4);

        /* Retrieve glyph offsets and advances directly into the output array
           to not have to allocate a temp buffer; the offsets then get
           converted to absolute positions. The renderLineGlyphPositionsInto()
           is aware of this and will make sure to read the input before writing
           to it. Taking every fourth item as the positions are subsequently
           in-place converted to quads by renderGlyphQuadsInto() below and
           putting them just into a prefix would cause them to be overwritten
           too early. */
        const Containers::StridedArrayView1D<Vertex> lineVertices = Containers::stridedArrayView(vertices).exceptPrefix(vertices.size() - shaper->glyphCount()*4);
        const Containers::StridedArrayView1D<Vector2> glyphOffsetsPositions = lineVertices.slice(&Vertex::position).every(4);
        const Containers::StridedArrayView1D<Vector2> glyphAdvances = lineVertices.slice(&Vertex::textureCoordinates).every(4);
        shaper->glyphOffsetsAdvancesInto(
            glyphOffsetsPositions,
            glyphAdvances);

        Vector2 cursor = linePosition;

        /* Render line glyph positions, aliasing the offsets */
        const Range2D lineRectangle = renderLineGlyphPositionsInto(
            font,
            size,
            /** @todo direction hardcoded here */
            LayoutDirection::HorizontalTopToBottom,
            glyphOffsetsPositions,
            glyphAdvances,
            cursor,
            glyphOffsetsPositions);

        /* Retrieve the glyph IDs directly into the output array, again to not
           have to allocate a temp buffer. The place where IDs get stored is
           where glyph advances were stored before and which were combined into
           glyph positions, and ultimately this location is where texture
           coordinates get written. Again the renderGlyphQuadsInto() is aware
           of this and will make sure to read the IDs before writing the quads.
           Again taking every fourth item as these are subsequently converted
           to quads by the function and putting them just into a prefix would
           cause them to be overwritten too early. */
        const Containers::StridedArrayView1D<UnsignedInt> glyphIds = Containers::arrayCast<UnsignedInt>(glyphAdvances);
        shaper->glyphIdsInto(glyphIds);

        /* Create quads from the positions */
        const Range2D lineQuadRectangle = renderGlyphQuadsInto(
            font,
            size,
            cache,
            glyphOffsetsPositions,
            glyphIds,
            lineVertices.slice(&Vertex::position),
            lineVertices.slice(&Vertex::textureCoordinates));

        /* Resolve the alignment based on what the shaper detected (if
           anything). Assume there are no font plugins that would produce
           vertical shape direction by default. */
        /** @todo drop all this once the shaper instance is configurable from
            outside */
        if(!resolvedAlignment) {
            const ShapeDirection shapeDirection = shaper->direction();
            CORRADE_INTERNAL_ASSERT(
                shapeDirection != ShapeDirection::TopToBottom &&
                shapeDirection != ShapeDirection::BottomToTop);
            resolvedAlignment = alignmentForDirection(alignment,
                /** @todo direction hardcoded here */
                LayoutDirection::HorizontalTopToBottom,
                shapeDirection);
        }

        /* Horizontally align the line, using either of the rectangles based on
           which alignment is desired */
        const Range2D alignedLineRectangle = alignRenderedLine(
            UnsignedByte(*resolvedAlignment) & Implementation::AlignmentGlyphBounds ?
                lineQuadRectangle : lineRectangle,
            /** @todo direction hardcoded here */
            LayoutDirection::HorizontalTopToBottom,
            *resolvedAlignment,
            lineVertices.slice(&Vertex::position));

        /* Extend the rectangle with final line bounds */
        rectangle = Math::join(rectangle, alignedLineRectangle);

    /* Move to next line */
    } while(prevPos = pos+1,
            linePosition -= lineAdvance,
            pos != std::string::npos);

    const Range2D alignedRectangle = alignRenderedBlock(
        rectangle,
        /** @todo direction hardcoded here */
        LayoutDirection::HorizontalTopToBottom,
        *resolvedAlignment,
        Containers::stridedArrayView(vertices).slice(&Vertex::position));

    return std::make_tuple(Utility::move(vertices), alignedRectangle);
}

std::pair<Containers::Array<char>, MeshIndexType> renderIndicesInternal(const UnsignedInt glyphCount) {
    const UnsignedInt vertexCount = glyphCount*4;
    const UnsignedInt indexCount = glyphCount*6;

    Containers::Array<char> indices;
    MeshIndexType indexType;
    if(vertexCount <= 256) {
        indexType = MeshIndexType::UnsignedByte;
        indices = Containers::Array<char>{NoInit, indexCount*sizeof(UnsignedByte)};
        renderGlyphQuadIndicesInto(0, Containers::arrayCast<UnsignedByte>(indices));
    } else if(vertexCount <= 65536) {
        indexType = MeshIndexType::UnsignedShort;
        indices = Containers::Array<char>{NoInit, indexCount*sizeof(UnsignedShort)};
        renderGlyphQuadIndicesInto(0, Containers::arrayCast<UnsignedShort>(indices));
    } else {
        indexType = MeshIndexType::UnsignedInt;
        indices = Containers::Array<char>{NoInit, indexCount*sizeof(UnsignedInt)};
        renderGlyphQuadIndicesInto(0, Containers::arrayCast<UnsignedInt>(indices));
    }

    return {Utility::move(indices), indexType};
}

std::tuple<GL::Mesh, Range2D> renderInternal(AbstractFont& font, const AbstractGlyphCache& cache, Float size, const std::string& text, GL::Buffer& vertexBuffer, GL::Buffer& indexBuffer, GL::BufferUsage usage, Alignment alignment) {
    /* Render vertices and upload them */
    std::vector<Vertex> vertices;
    Range2D rectangle;
    std::tie(vertices, rectangle) = renderVerticesInternal(font, cache, size, text, alignment);
    vertexBuffer.setData(vertices, usage);

    const UnsignedInt glyphCount = vertices.size()/4;
    const UnsignedInt indexCount = glyphCount*6;

    /* Render indices and upload them */
    Containers::Array<char> indices;
    MeshIndexType indexType;
    std::tie(indices, indexType) = renderIndicesInternal(glyphCount);
    indexBuffer.setData(indices, usage);

    /* Configure mesh except for vertex buffer (depends on dimension count, done
       in subclass) */
    GL::Mesh mesh;
    mesh.setPrimitive(MeshPrimitive::Triangles)
        .setCount(indexCount)
        .setIndexBuffer(indexBuffer, 0, indexType, 0, vertices.size());

    return std::make_tuple(Utility::move(mesh), rectangle);
}

}

std::tuple<std::vector<Vector2>, std::vector<Vector2>, std::vector<UnsignedInt>, Range2D> AbstractRenderer::render(AbstractFont& font, const AbstractGlyphCache& cache, Float size, const std::string& text, Alignment alignment) {
    /* Render vertices */
    std::vector<Vertex> vertices;
    Range2D rectangle;
    std::tie(vertices, rectangle) = renderVerticesInternal(font, cache, size, text, alignment);

    /* Deinterleave the vertices */
    std::vector<Vector2> positions, textureCoordinates;
    positions.reserve(vertices.size());
    positions.reserve(textureCoordinates.size());
    for(const auto& v: vertices) {
        positions.push_back(v.position);
        textureCoordinates.push_back(v.textureCoordinates);
    }

    /* Render indices */
    const UnsignedInt glyphCount = vertices.size()/4;
    std::vector<UnsignedInt> indices(glyphCount*6);
    renderGlyphQuadIndicesInto(0, indices);

    return std::make_tuple(Utility::move(positions), Utility::move(textureCoordinates), Utility::move(indices), rectangle);
}

template<UnsignedInt dimensions> std::tuple<GL::Mesh, Range2D> Renderer<dimensions>::render(AbstractFont& font, const AbstractGlyphCache& cache, Float size, const std::string& text, GL::Buffer& vertexBuffer, GL::Buffer& indexBuffer, GL::BufferUsage usage, Alignment alignment) {
    /* Finalize mesh configuration and return the result */
    auto r = renderInternal(font, cache, size, text, vertexBuffer, indexBuffer, usage, alignment);
    GL::Mesh& mesh = std::get<0>(r);
    mesh.addVertexBuffer(vertexBuffer, 0,
        typename Shaders::GenericGL<dimensions>::Position(
            Shaders::GenericGL<dimensions>::Position::Components::Two),
        typename Shaders::GenericGL<dimensions>::TextureCoordinates());
    return r;
}

#if defined(MAGNUM_TARGET_GLES2) && !defined(CORRADE_TARGET_EMSCRIPTEN)
AbstractRenderer::BufferMapImplementation AbstractRenderer::bufferMapImplementation = &AbstractRenderer::bufferMapImplementationFull;
AbstractRenderer::BufferUnmapImplementation AbstractRenderer::bufferUnmapImplementation = &AbstractRenderer::bufferUnmapImplementationDefault;

void* AbstractRenderer::bufferMapImplementationFull(GL::Buffer& buffer, GLsizeiptr) {
    return buffer.map(GL::Buffer::MapAccess::WriteOnly);
}
#endif

#if !defined(MAGNUM_TARGET_GLES2) || defined(CORRADE_TARGET_EMSCRIPTEN)
inline void* AbstractRenderer::bufferMapImplementation(GL::Buffer& buffer, GLsizeiptr length)
#else
void* AbstractRenderer::bufferMapImplementationRange(GL::Buffer& buffer, GLsizeiptr length)
#endif
{
    #ifndef CORRADE_TARGET_EMSCRIPTEN
    return buffer.map(0, length, GL::Buffer::MapFlag::InvalidateBuffer|GL::Buffer::MapFlag::Write);
    #else
    static_cast<void>(length);
    return &buffer == &_indexBuffer ? _indexBufferData : _vertexBufferData;
    #endif
}

#if !defined(MAGNUM_TARGET_GLES2) || defined(CORRADE_TARGET_EMSCRIPTEN)
inline void AbstractRenderer::bufferUnmapImplementation(GL::Buffer& buffer)
#else
void AbstractRenderer::bufferUnmapImplementationDefault(GL::Buffer& buffer)
#endif
{
    #ifndef CORRADE_TARGET_EMSCRIPTEN
    buffer.unmap();
    #else
    buffer.setSubData(0, &buffer == &_indexBuffer ? _indexBufferData : _vertexBufferData);
    #endif
}

AbstractRenderer::AbstractRenderer(AbstractFont& font, const AbstractGlyphCache& cache, const Float size, const Alignment alignment): _vertexBuffer{GL::Buffer::TargetHint::Array}, _indexBuffer{GL::Buffer::TargetHint::ElementArray}, font(font), cache(cache), _fontSize{size}, _alignment(alignment), _capacity(0) {
    #ifndef MAGNUM_TARGET_GLES
    MAGNUM_ASSERT_GL_EXTENSION_SUPPORTED(GL::Extensions::ARB::map_buffer_range);
    #elif defined(MAGNUM_TARGET_GLES2) && !defined(CORRADE_TARGET_EMSCRIPTEN)
    if(GL::Context::current().isExtensionSupported<GL::Extensions::EXT::map_buffer_range>()) {
        bufferMapImplementation = &AbstractRenderer::bufferMapImplementationRange;
    } else {
        MAGNUM_ASSERT_GL_EXTENSION_SUPPORTED(GL::Extensions::OES::mapbuffer);
        Warning() << "Text::Renderer:" << GL::Extensions::EXT::map_buffer_range::string()
                  << "is not supported, using inefficient" << GL::Extensions::OES::mapbuffer::string()
                  << "instead";
    }
    #endif

    /* Vertex buffer configuration depends on dimension count, done in subclass */
    _mesh.setPrimitive(MeshPrimitive::Triangles);
}

AbstractRenderer::~AbstractRenderer() = default;

template<UnsignedInt dimensions> Renderer<dimensions>::Renderer(AbstractFont& font, const AbstractGlyphCache& cache, const Float size, const Alignment alignment): AbstractRenderer(font, cache, size, alignment) {
    /* Finalize mesh configuration */
    _mesh.addVertexBuffer(_vertexBuffer, 0,
        typename Shaders::GenericGL<dimensions>::Position(
            Shaders::GenericGL<dimensions>::Position::Components::Two),
        typename Shaders::GenericGL<dimensions>::TextureCoordinates());
}

void AbstractRenderer::reserve(const uint32_t glyphCount, const GL::BufferUsage vertexBufferUsage, const GL::BufferUsage indexBufferUsage) {
    _capacity = glyphCount;

    const UnsignedInt vertexCount = glyphCount*4;

    /* Allocate vertex buffer, reset vertex count */
    _vertexBuffer.setData({nullptr, vertexCount*sizeof(Vertex)}, vertexBufferUsage);
    #ifdef CORRADE_TARGET_EMSCRIPTEN
    _vertexBufferData = Containers::Array<UnsignedByte>(vertexCount*sizeof(Vertex));
    #endif
    _mesh.setCount(0);

    /* Render indices */
    Containers::Array<char> indexData;
    MeshIndexType indexType;
    std::tie(indexData, indexType) = renderIndicesInternal(glyphCount);

    /* Allocate index buffer, reset index count and reconfigure buffer binding */
    _indexBuffer.setData({nullptr, indexData.size()}, indexBufferUsage);
    #ifdef CORRADE_TARGET_EMSCRIPTEN
    _indexBufferData = Containers::Array<UnsignedByte>(indexData.size());
    #endif
    _mesh.setCount(0)
        .setIndexBuffer(_indexBuffer, 0, indexType, 0, vertexCount);

    /* Prefill index buffer */
    char* const indices = static_cast<char*>(bufferMapImplementation(_indexBuffer, indexData.size()));
    CORRADE_INTERNAL_ASSERT(indices);
    /** @todo Emscripten: it can be done without this copying altogether */
    std::copy(indexData.begin(), indexData.end(), indices);
    bufferUnmapImplementation(_indexBuffer);
}

void AbstractRenderer::render(const std::string& text) {
    /* Render vertex data */
    std::vector<Vertex> vertexData;
    _rectangle = {};
    std::tie(vertexData, _rectangle) = renderVerticesInternal(font, cache, _fontSize, text, _alignment);

    const UnsignedInt glyphCount = vertexData.size()/4;
    const UnsignedInt vertexCount = glyphCount*4;
    const UnsignedInt indexCount = glyphCount*6;

    CORRADE_ASSERT(glyphCount <= _capacity,
        "Text::Renderer::render(): capacity" << _capacity << "too small to render" << glyphCount << "glyphs", );

    /* Interleave the data into mapped buffer*/
    Containers::ArrayView<Vertex> vertices(static_cast<Vertex*>(bufferMapImplementation(_vertexBuffer,
        vertexCount*sizeof(Vertex))), vertexCount);
    CORRADE_INTERNAL_ASSERT_OUTPUT(vertices);
    std::copy(vertexData.begin(), vertexData.end(), vertices.begin());
    bufferUnmapImplementation(_vertexBuffer);

    /* Update index count */
    _mesh.setCount(indexCount);
}

template class MAGNUM_TEXT_EXPORT Renderer<2>;
template class MAGNUM_TEXT_EXPORT Renderer<3>;
#endif

}}