TextureTools: ported distanceField() to OpenGL 2.1 and OpenGL ES.

* Older GLSL doesn't have texelFetch() and related things, working
   around it by using classical texture() and normalized floating-point
   coordinates. But that needs to have Texture::imageSize() passed,
   which is not available in OpenGL ES, thus the user must specify it
   explicitly there. On desktop OpenGL that parameter is ignored.
 * Older GLSL doesn't have gl_VertexID, thus vertex buffer must be
   created and vertex data passed expliticly.
 * GLSL ES 2.0 doesn't have one-component texture format and
   TextureFormat::Luminance probably isn't renderable anywhere, thus
   TextureFormat::RGB should be used, although it is inefficient.
 * Checking  for framebuffer completeness, if not complete, nothing is
   done.
 * Re-eabled building of TextureTools library in all ES PKGBUILDs.

PKGBUILD-es2

@@ -27,7 +27,6 @@ build() {
         -DTARGET_GLES=ON \
         -DTARGET_GLES2=ON \
         -DWITH_TEXT=OFF \
-        -DWITH_TEXTURETOOLS=OFF \
         -DWITH_MAGNUMINFO=OFF \
         -DWITH_XEGLAPPLICATION=ON
     make

PKGBUILD-es2desktop

@@ -28,7 +28,6 @@ build() {
         -DTARGET_GLES2=ON \
         -DTARGET_DESKTOP_GLES=ON \
         -DWITH_TEXT=OFF \
-        -DWITH_TEXTURETOOLS=OFF \
         -DWITH_MAGNUMINFO=OFF \
         -DWITH_XEGLAPPLICATION=ON
     make

PKGBUILD-es3

@@ -27,7 +27,6 @@ build() {
         -DTARGET_GLES=ON \
         -DTARGET_GLES2=OFF \
         -DWITH_TEXT=OFF \
-        -DWITH_TEXTURETOOLS=OFF \
         -DWITH_MAGNUMINFO=OFF \
         -DWITH_XEGLAPPLICATION=ON
     make

src/Text/DistanceFieldGlyphCache.cpp

@@ -57,7 +57,7 @@ void DistanceFieldGlyphCache::setImage(const Vector2i& offset, Image2D* const im
         ->setImage(0, internalFormat, image);
 
     /* Create distance field from input texture */
-    TextureTools::distanceField(&input, &_texture, Rectanglei::fromSize(offset*scale, image->size()*scale), radius);
+    TextureTools::distanceField(&input, &_texture, Rectanglei::fromSize(offset*scale, image->size()*scale), radius, image->size());
 }
 
 void DistanceFieldGlyphCache::setDistanceFieldImage(const Vector2i& offset, Image2D* const image) {

src/TextureTools/DistanceField.cpp

@@ -39,6 +39,8 @@ namespace {
 
 class DistanceFieldShader: public AbstractShaderProgram {
     public:
+        typedef Attribute<0, Vector2> Position;
+
         enum: Int {
             TextureLayer = 8
         };
@@ -50,62 +52,148 @@ class DistanceFieldShader: public AbstractShaderProgram {
             return this;
         }
 
-        DistanceFieldShader* setScaling(Vector2 scaling) {
+        DistanceFieldShader* setScaling(const Vector2& scaling) {
             setUniform(scalingUniform, scaling);
             return this;
         }
 
+        DistanceFieldShader* setImageSizeInverted(const Vector2& size) {
+            setUniform(imageSizeInvertedUniform, size);
+            return this;
+        }
+
     private:
-        static const Int radiusUniform = 0,
-            scalingUniform = 1;
+        Int radiusUniform,
+            scalingUniform,
+            imageSizeInvertedUniform;
 };
 
-DistanceFieldShader::DistanceFieldShader() {
-    MAGNUM_ASSERT_VERSION_SUPPORTED(Version::GL330);
-    MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::ARB::explicit_attrib_location);
-    MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::ARB::explicit_uniform_location);
-    MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::ARB::shading_language_420pack);
-
-    /** @todo compatibility! */
-
+DistanceFieldShader::DistanceFieldShader(): radiusUniform(0), scalingUniform(1) {
     Utility::Resource rs("MagnumTextureTools");
 
-    Shader vert(Version::GL330, Shader::Type::Vertex);
-    vert.addSource(rs.get("DistanceFieldShader.vert"));
+    #ifndef MAGNUM_TARGET_GLES
+    const Version v = Context::current()->supportedVersion({Version::GL320, Version::GL300, Version::GL210});
+    #else
+    const Version v = Context::current()->supportedVersion({Version::GLES300, Version::GLES200});
+    #endif
+
+    Shader vert(v, Shader::Type::Vertex);
+    vert.addSource(rs.get("compatibility.glsl"))
+        .addSource(rs.get("DistanceFieldShader.vert"));
     CORRADE_INTERNAL_ASSERT_OUTPUT(vert.compile());
     attachShader(vert);
 
-    Shader frag(Version::GL330, Shader::Type::Fragment);
+    Shader frag(v, Shader::Type::Fragment);
     frag.addSource(rs.get("compatibility.glsl"))
         .addSource(rs.get("DistanceFieldShader.frag"));
     CORRADE_INTERNAL_ASSERT_OUTPUT(frag.compile());
     attachShader(frag);
 
+    /* Older GLSL doesn't have gl_VertexID, vertices must be supplied explicitly */
+    #ifndef MAGNUM_TARGET_GLES
+    if(!Context::current()->isVersionSupported(Version::GL300))
+    #else
+    if(!Context::current()->isVersionSupported(Version::GLES300))
+    #endif
+    {
+        bindAttributeLocation(Position::Location, "position");
+    }
+
     CORRADE_INTERNAL_ASSERT_OUTPUT(link());
-}
 
+    #ifndef MAGNUM_TARGET_GLES
+    if(!Context::current()->isExtensionSupported<Extensions::GL::ARB::explicit_uniform_location>())
+    #endif
+    {
+        radiusUniform = uniformLocation("radius");
+        scalingUniform = uniformLocation("scaling");
+
+        #ifndef MAGNUM_TARGET_GLES
+        if(!Context::current()->isVersionSupported(Version::GL300))
+        #else
+        if(!Context::current()->isVersionSupported(Version::GLES300))
+        #endif
+        {
+            imageSizeInvertedUniform = uniformLocation("imageSizeInverted");
+        }
+    }
+
+    #ifndef MAGNUM_TARGET_GLES
+    if(!Context::current()->isExtensionSupported<Extensions::GL::ARB::shading_language_420pack>())
+    #endif
+    {
+        setUniform(uniformLocation("textureData"), TextureLayer);
+    }
 }
 
-void distanceField(Texture2D* input, Texture2D* output, const Rectanglei& rectangle, const Int radius) {
-    MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::EXT::framebuffer_object);
+}
+#ifndef MAGNUM_TARGET_GLES
+void distanceField(Texture2D* input, Texture2D* output, const Rectanglei& rectangle, const Int radius, const Vector2i&)
+#else
+void distanceField(Texture2D* input, Texture2D* output, const Rectanglei& rectangle, const Int radius, const Vector2i& imageSize)
+#endif
+{
+    #ifndef MAGNUM_TARGET_GLES
+    MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::ARB::framebuffer_object);
+    #endif
 
     /** @todo Disable depth test, blending and then enable it back (if was previously) */
 
+    #ifndef MAGNUM_TARGET_GLES
+    Vector2i imageSize = input->imageSize(0);
+    #endif
+
     Framebuffer framebuffer(rectangle);
     framebuffer.attachTexture2D(Framebuffer::ColorAttachment(0), output, 0);
     framebuffer.bind(FramebufferTarget::Draw);
+    framebuffer.clear(FramebufferClear::Color);
+
+    const Framebuffer::Status status = framebuffer.checkStatus(FramebufferTarget::Draw);
+    if(status != Framebuffer::Status::Complete) {
+        Error() << "TextureTools::distanceField(): cannot render to given output texture, unexpected framebuffer status"
+                << status;
+        return;
+    }
 
     DistanceFieldShader shader;
     shader.setRadius(radius)
-        ->setScaling(Vector2(input->imageSize(0))/rectangle.size())
+        ->setScaling(Vector2(imageSize)/rectangle.size())
         ->use();
 
     input->bind(DistanceFieldShader::TextureLayer);
 
+    #ifndef MAGNUM_TARGET_GLES
+    if(!Context::current()->isVersionSupported(Version::GL300))
+    #else
+    if(!Context::current()->isVersionSupported(Version::GLES300))
+    #endif
+    {
+        shader.setImageSizeInverted(Vector2(1)/imageSize);
+    }
+
     Mesh mesh;
     mesh.setPrimitive(Mesh::Primitive::Triangles)
-        ->setVertexCount(3)
-        ->draw();
+        ->setVertexCount(3);
+
+    /* Older GLSL doesn't have gl_VertexID, vertices must be supplied explicitly */
+    Buffer buffer;
+    #ifndef MAGNUM_TARGET_GLES
+    if(!Context::current()->isVersionSupported(Version::GL300))
+    #else
+    if(!Context::current()->isVersionSupported(Version::GLES300))
+    #endif
+    {
+        constexpr Vector2 triangle[] = {
+            Vector2(-1.0,  1.0),
+            Vector2(-1.0, -3.0),
+            Vector2( 3.0,  1.0)
+        };
+        buffer.setData(triangle, Buffer::Usage::StaticDraw);
+        mesh.addVertexBuffer(&buffer, 0, DistanceFieldShader::Position());
+    }
+
+    /* Draw the mesh */
+    mesh.draw();
 }
 
 }}

src/TextureTools/DistanceField.h

@@ -28,6 +28,9 @@
  * @brief Function Magnum::TextureTools::distanceField()
  */
 
+#ifndef MAGNUM_TARGET_GLES
+#include "Math/Vector2.h"
+#endif
 #include "Magnum.h"
 
 #include "TextureTools/magnumTextureToolsVisibility.h"
@@ -40,6 +43,8 @@ namespace Magnum { namespace TextureTools {
 @param output       Output texture
 @param rectangle    Rectangle in output texture where to render
 @param radius       Max lookup radius in input texture
+@param imageSize    Input texture size. Needed only in OpenGL ES, in desktop
+    OpenGL the information is gathered automatically using Texture::imageSize().
 
 Converts binary image (stored in red channel of @p input) to signed distance
 field (stored in red channel in @p rectangle of @p output). The purpose of this
@@ -66,8 +71,21 @@ and Special Effects, SIGGRAPH 2007,
 http://www.valvesoftware.com/publications/2007/SIGGRAPH2007_AlphaTestedMagnification.pdf*
 
 @attention This is GPU-only implementation, so it expects active context.
+
+@note If internal format of @p output texture is not renderable, this function
+    prints message to error output and does nothing. In desktop OpenGL and
+    OpenGL ES 3.0 it's common to render to @ref TextureFormat "TextureFormat::R8".
+    In OpenGL ES 2.0 you can use @ref TextureFormat "TextureFormat::Red" if
+    @es_extension{EXT,texture_rg} is available, if not, the smallest but still
+    inefficient supported format is in most cases @ref TextureFormat "TextureFormat::RGB",
+    rendering to @ref TextureFormat "TextureFormat::Luminance" is not supported
+    in most cases.
 */
-void MAGNUM_TEXTURETOOLS_EXPORT distanceField(Texture2D* input, Texture2D* output, const Rectanglei& rectangle, Int radius);
+#ifndef MAGNUM_TARGET_GLES
+void MAGNUM_TEXTURETOOLS_EXPORT distanceField(Texture2D* input, Texture2D* output, const Rectanglei& rectangle, Int radius, const Vector2i& imageSize = Vector2i());
+#else
+void MAGNUM_TEXTURETOOLS_EXPORT distanceField(Texture2D* input, Texture2D* output, const Rectanglei& rectangle, Int radius, const Vector2i& imageSize);
+#endif
 
 }}
 

src/TextureTools/DistanceFieldShader.frag

@@ -22,40 +22,90 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+#ifndef NEW_GLSL
+#define in varying
+#define value gl_FragColor.x
+#define const
+#define texture texture2D
+#endif
+
+#if (defined(GL_ES) && __VERSION__ >= 300) || (!defined(GL_ES) && __VERSION__ >= 150)
+#define TEXELFETCH_USABLE
+#endif
+
+#ifdef EXPLICIT_UNIFORM_LOCATION
 layout(location = 0) uniform int radius;
 layout(location = 1) uniform vec2 scaling;
-layout(binding = 8) uniform sampler2D texture;
-
-layout(pixel_center_integer) in vec4 gl_FragCoord;
-
-out float value;
+layout(binding = 8) uniform sampler2D textureData;
+#else
+uniform lowp int radius;
+uniform mediump vec2 scaling;
+uniform lowp sampler2D textureData;
+#endif
+
+#ifdef TEXELFETCH_USABLE
+layout(pixel_center_integer) in mediump vec4 gl_FragCoord;
+#else
+#ifdef EXPLICIT_UNIFORM_LOCATION
+layout(location = 2) uniform vec2 imageSizeInverted;
+#else
+uniform mediump vec2 imageSizeInverted;
+#endif
+#endif
+
+#ifdef NEW_GLSL
+out lowp float value;
+#endif
+
+#ifdef TEXELFETCH_USABLE
+mediump ivec2 rotate(const mediump ivec2 vec) {
+    return mediump ivec2(-vec.y, vec.x);
+}
 
-ivec2 rotate(const ivec2 vec) {
-    return ivec2(-vec.y, vec.x);
+bool hasValue(const mediump ivec2 position, const mediump ivec2 offset) {
+    return texelFetch(textureData, position+offset, 0).r > 0.5;
+}
+#else
+mediump vec2 rotate(const mediump vec2 vec) {
+    return mediump vec2(-vec.y, vec.x);
 }
 
-bool hasValue(const ivec2 position, const ivec2 offset) {
-    return texelFetch(texture, position+offset, 0).r > 0.5;
+bool hasValue(const mediump vec2 position, const mediump vec2 offset) {
+    return texture(textureData, position+offset).r > 0.5;
 }
+#endif
 
 void main() {
-    const ivec2 position = ivec2(gl_FragCoord.xy*scaling);
+    #ifdef TEXELFETCH_USABLE
+    const mediump ivec2 position = ivec2(gl_FragCoord.xy*scaling);
+    #else
+    const mediump vec2 position = gl_FragCoord.xy*scaling*imageSizeInverted;
+    #endif
 
     /* If pixel at the position is inside (1), we are looking for nearest pixel
        outside and the value will be positive (> 0.5). If it is outside (0), we
        are looking for nearest pixel inside and the value will be negative
        (< 0.5). */
+    #ifdef TEXELFETCH_USABLE
     const bool isInside = hasValue(position, ivec2(0, 0));
-    const float sign = isInside ? 1.0 : -1.0;
+    #else
+    const bool isInside = hasValue(position, vec2(0.0, 0.0));
+    #endif
+    const highp float sign = isInside ? 1.0 : -1.0;
 
     /* Minimal found distance is just out of the radius (i.e. infinity) */
-    float minDistanceSquared = float((radius+1)*(radius+1));
+    highp float minDistanceSquared = float((radius+1)*(radius+1));
 
     /* Go in circles around the point and find nearest value */
     int radiusLimit = radius;
     for(int i = 1; i <= radiusLimit; ++i) {
         for(int j = 0, jmax = i*2; j != jmax; ++j) {
-            const ivec2 offset = {-i+j, i};
+            #ifdef TEXELFETCH_USABLE
+            const lowp ivec2 offset = ivec2(-i+j, i);
+            #else
+            const lowp vec2 pixelOffset = vec2(float(-i+j), float(i));
+            const lowp vec2 offset = pixelOffset*imageSizeInverted;
+            #endif
 
             /* If any of the four values is opposite of what is on the pixel,
                we found nearest value */
@@ -63,7 +113,11 @@ void main() {
                hasValue(position, rotate(offset)) == !isInside ||
                hasValue(position, rotate(rotate(offset))) == !isInside ||
                hasValue(position, rotate(rotate(rotate(offset)))) == !isInside) {
-                const float distanceSquared = dot(vec2(offset), vec2(offset));
+                #ifdef TEXELFETCH_USABLE
+                const mediump float distanceSquared = dot(vec2(offset), vec2(offset));
+                #else
+                const mediump float distanceSquared = dot(pixelOffset, pixelOffset);
+                #endif
 
                 /* Set smaller distance, if found, or continue with lookup for
                    smaller */
@@ -73,7 +127,11 @@ void main() {
                 /* Set radius limit to max radius which can contain smaller
                    value, e.g. for distance 3.5 we can find smaller value even
                    in radius 3 */
+                #ifdef NEW_GLSL
                 radiusLimit = min(radius, int(floor(length(vec2(offset)))));
+                #else
+                radiusLimit = int(min(float(radius), floor(length(vec2(offset)))));
+                #endif
             }
         }
     }

src/TextureTools/DistanceFieldShader.vert

@@ -22,7 +22,15 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+#ifndef NEW_GLSL
+attribute lowp vec4 position;
+#endif
+
 void main() {
+    #ifdef NEW_GLSL
     gl_Position = vec4((gl_VertexID == 2) ?  3.0 : -1.0,
                        (gl_VertexID == 1) ? -3.0 :  1.0, 0.0, 1.0);
+    #else
+    gl_Position = position;
+    #endif
 }