Text: introduce font ascent and descent.

It required some ABI-incompatible changes so I bumped the font and
font converter plugin interface strings to avoid crashes at runtime.

src/Magnum/Text/AbstractFont.cpp

@@ -45,12 +45,16 @@ bool AbstractFont::openData(const std::vector<std::pair<std::string, Containers:
         "Text::AbstractFont::openData(): no data passed", false);
 
     close();
-    std::tie(_size, _lineHeight) = doOpenData(data, size);
-    CORRADE_INTERNAL_ASSERT(isOpened() || (_size == 0.0f && _lineHeight == 0.0f));
+    const Metrics metrics = doOpenData(data, size);
+    _size = metrics.size;
+    _ascent = metrics.ascent;
+    _descent = metrics.descent;
+    _lineHeight = metrics.lineHeight;
+    CORRADE_INTERNAL_ASSERT(isOpened() || (!_size && !_ascent && !_descent && !_lineHeight));
     return isOpened();
 }
 
-std::pair<Float, Float> AbstractFont::doOpenData(const std::vector<std::pair<std::string, Containers::ArrayView<const char>>>& data, const Float size) {
+auto AbstractFont::doOpenData(const std::vector<std::pair<std::string, Containers::ArrayView<const char>>>& data, const Float size) -> Metrics {
     CORRADE_ASSERT(!(features() & Feature::MultiFile),
         "Text::AbstractFont::openData(): feature advertised but not implemented", {});
     CORRADE_ASSERT(data.size() == 1,
@@ -67,24 +71,32 @@ bool AbstractFont::openSingleData(const Containers::ArrayView<const char> data,
         "Text::AbstractFont::openSingleData(): the format is not single-file", false);
 
     close();
-    std::tie(_size, _lineHeight) = doOpenSingleData(data, size);
-    CORRADE_INTERNAL_ASSERT(isOpened() || (_size == 0.0f && _lineHeight == 0.0f));
+    const Metrics metrics = doOpenSingleData(data, size);
+    _size = metrics.size;
+    _ascent = metrics.ascent;
+    _descent = metrics.descent;
+    _lineHeight = metrics.lineHeight;
+    CORRADE_INTERNAL_ASSERT(isOpened() || (!_size && !_ascent && !_descent && !_lineHeight));
     return isOpened();
 }
 
-std::pair<Float, Float> AbstractFont::doOpenSingleData(Containers::ArrayView<const char>, Float) {
+auto AbstractFont::doOpenSingleData(Containers::ArrayView<const char>, Float) -> Metrics {
     CORRADE_ASSERT(false, "Text::AbstractFont::openSingleData(): feature advertised but not implemented", {});
     return {};
 }
 
 bool AbstractFont::openFile(const std::string& filename, const Float size) {
     close();
-    std::tie(_size, _lineHeight) = doOpenFile(filename, size);
-    CORRADE_INTERNAL_ASSERT(isOpened() || (_size == 0.0f && _lineHeight == 0.0f));
+    const Metrics metrics = doOpenFile(filename, size);
+    _size = metrics.size;
+    _ascent = metrics.ascent;
+    _descent = metrics.descent;
+    _lineHeight = metrics.lineHeight;
+    CORRADE_INTERNAL_ASSERT(isOpened() || (!_size && !_ascent && !_descent && !_lineHeight));
     return isOpened();
 }
 
-std::pair<Float, Float> AbstractFont::doOpenFile(const std::string& filename, const Float size) {
+auto AbstractFont::doOpenFile(const std::string& filename, const Float size) -> Metrics {
     CORRADE_ASSERT(features() & Feature::OpenData && !(features() & Feature::MultiFile),
         "Text::AbstractFont::openFile(): not implemented", {});
 

src/Magnum/Text/AbstractFont.h

@@ -72,10 +72,10 @@ checked by the implementation:
 -   All `do*()` implementations working on opened file are called only if
     there is any file opened.
 
-Plugin interface string is `"cz.mosra.magnum.Text.AbstractFont/0.2.3"`.
+Plugin interface string is `"cz.mosra.magnum.Text.AbstractFont/0.2.4"`.
 */
 class MAGNUM_TEXT_EXPORT AbstractFont: public PluginManager::AbstractPlugin {
-    CORRADE_PLUGIN_INTERFACE("cz.mosra.magnum.Text.AbstractFont/0.2.3")
+    CORRADE_PLUGIN_INTERFACE("cz.mosra.magnum.Text.AbstractFont/0.2.4")
 
     public:
         /**
@@ -158,16 +158,33 @@ class MAGNUM_TEXT_EXPORT AbstractFont: public PluginManager::AbstractPlugin {
         /**
          * @brief Font size
          *
-         * Returns scale in which @ref lineHeight() and @ref glyphAdvance() is
-         * returned.
+         * Returns scale in which @ref lineHeight(), @ref ascent(),
+         * @ref descent() and @ref glyphAdvance() is returned.
          */
         Float size() const { return _size; }
 
+        /**
+         * @brief Font ascent
+         *
+         * Distance from baseline to top, scaled to font size. Positive value.
+         * @see @ref size(), @ref descent(), @ref lineHeight()
+         */
+        Float ascent() const { return _ascent; }
+
+        /**
+         * @brief Font descent
+         *
+         * Distance from baseline to bottom, scalled to font size. Negative
+         * value.
+         * @see @ref size(), @ref ascent(), @ref lineHeight()
+         */
+        Float descent() const { return _descent; }
+
         /**
          * @brief Line height
          *
          * Returns line height scaled to font size.
-         * @see @ref size()
+         * @see @ref size(), @ref ascent(), @ref descent()
          */
         Float lineHeight() const { return _lineHeight; }
 
@@ -225,6 +242,38 @@ class MAGNUM_TEXT_EXPORT AbstractFont: public PluginManager::AbstractPlugin {
          */
         std::unique_ptr<AbstractLayouter> layout(const GlyphCache& cache, Float size, const std::string& text);
 
+    protected:
+        /**
+         * @brief Font metrics
+         *
+         * @see @ref doOpenFile(), @ref doOpenData(), @ref doOpenSingleData()
+         */
+        struct Metrics {
+            /**
+             * Font size
+             * @see @ref size()
+             */
+            Float size;
+
+            /**
+             * Font ascent
+             * @see @ref ascent()
+             */
+            Float ascent;
+
+            /**
+             * Font descent
+             * @see @ref descent()
+             */
+            Float descent;
+
+            /**
+             * Line height
+             * @see @ref lineHeight()
+             */
+            Float lineHeight;
+        };
+
     #ifdef DOXYGEN_GENERATING_OUTPUT
     protected:
     #else
@@ -239,29 +288,29 @@ class MAGNUM_TEXT_EXPORT AbstractFont: public PluginManager::AbstractPlugin {
         /**
          * @brief Implementation for @ref openData()
          *
-         * Return size and line height of opened font on successful opening,
-         * zeros otherwise. If the plugin doesn't have @ref Feature::MultiFile,
+         * Return metrics of opened font on successful opening, zeros
+         * otherwise. If the plugin doesn't have @ref Feature::MultiFile,
          * default implementation calls @ref doOpenSingleData().
          */
-        virtual std::pair<Float, Float> doOpenData(const std::vector<std::pair<std::string, Containers::ArrayView<const char>>>& data, Float size);
+        virtual Metrics doOpenData(const std::vector<std::pair<std::string, Containers::ArrayView<const char>>>& data, Float size);
 
         /**
          * @brief Implementation for @ref openSingleData()
          *
-         * Return size and line height of opened font on successful opening,
-         * zeros otherwise.
+         * Return metrics of opened font on successful opening, zeros
+         * otherwise.
          */
-        virtual std::pair<Float, Float> doOpenSingleData(Containers::ArrayView<const char> data, Float size);
+        virtual Metrics doOpenSingleData(Containers::ArrayView<const char> data, Float size);
 
         /**
          * @brief Implementation for @ref openFile()
          *
-         * Return size and line height of opened font on successful opening,
-         * zeros otherwise. If @ref Feature::OpenData is supported and the
-         * plugin doesn't have @ref Feature::MultiFile, default implementation
-         * opens the file and calls @ref doOpenSingleData() with its contents.
+         * Return metrics of opened font on successful opening, zeros
+         * otherwise. If @ref Feature::OpenData is supported and the plugin
+         * doesn't have @ref Feature::MultiFile, default implementation opens
+         * the file and calls @ref doOpenSingleData() with its contents.
          */
-        virtual std::pair<Float, Float> doOpenFile(const std::string& filename, Float size);
+        virtual Metrics doOpenFile(const std::string& filename, Float size);
 
         /** @brief Implementation for @ref close() */
         virtual void doClose() = 0;
@@ -289,7 +338,7 @@ class MAGNUM_TEXT_EXPORT AbstractFont: public PluginManager::AbstractPlugin {
     #ifdef DOXYGEN_GENERATING_OUTPUT
     private:
     #endif
-        Float _size, _lineHeight;
+        Float _size, _ascent, _descent, _lineHeight;
 };
 
 CORRADE_ENUMSET_OPERATORS(AbstractFont::Features)

src/Magnum/Text/AbstractFontConverter.h

@@ -68,10 +68,10 @@ checked by the implementation:
 -   Function `doImport*FromData()` is called only if there is at least one data
     array passed.
 
-Plugin interface string is `"cz.mosra.magnum.Text.AbstractFontConverter/0.1.1"`.
+Plugin interface string is `"cz.mosra.magnum.Text.AbstractFontConverter/0.1.2"`.
 */
 class MAGNUM_TEXT_EXPORT AbstractFontConverter: public PluginManager::AbstractPlugin {
-    CORRADE_PLUGIN_INTERFACE("cz.mosra.magnum.Text.AbstractFontConverter/0.1.1")
+    CORRADE_PLUGIN_INTERFACE("cz.mosra.magnum.Text.AbstractFontConverter/0.1.2")
 
     public:
         /**

src/Magnum/Text/Test/AbstractFontTest.cpp

@@ -56,7 +56,7 @@ class SingleDataFont: public Text::AbstractFont {
         bool doIsOpened() const override { return opened; }
         void doClose() override {}
 
-        std::pair<Float, Float> doOpenSingleData(const Containers::ArrayView<const char> data, Float) override {
+        Metrics doOpenSingleData(const Containers::ArrayView<const char> data, Float) override {
             opened = (data.size() == 1 && data[0] == '\xa5');
             return {};
         }

src/Magnum/Text/Test/RendererGLTest.cpp

@@ -344,9 +344,9 @@ void RendererGLTest::multiline() {
             bool doIsOpened() const override { return _opened; }
             void doClose() override { _opened = false; }
 
-            std::pair<Float, Float> doOpenFile(const std::string&, Float) override {
+            Metrics doOpenFile(const std::string&, Float) override {
                 _opened = true;
-                return {0.5f, 0.75f};
+                return {0.5f, 0.45f, -0.25f, 0.75f};
             }
 
             UnsignedInt doGlyphId(char32_t) override { return 0; }
@@ -370,6 +370,8 @@ void RendererGLTest::multiline() {
     /* We're rendering text at 2.0f size and the font is scaled to 0.3f, so the
        line advance should be 0.75f*2.0f/0.5f = 3.0f */
     CORRADE_COMPARE(font.size(), 0.5f);
+    CORRADE_COMPARE(font.ascent(), 0.45f);
+    CORRADE_COMPARE(font.descent(), -0.25f);
     CORRADE_COMPARE(font.lineHeight(), 0.75f);
 
     /* Bounds */

src/MagnumPlugins/MagnumFont/MagnumFont.cpp

@@ -68,7 +68,7 @@ auto MagnumFont::doFeatures() const -> Features { return Feature::OpenData|Featu
 
 bool MagnumFont::doIsOpened() const { return _opened; }
 
-std::pair<Float, Float> MagnumFont::doOpenData(const std::vector<std::pair<std::string, Containers::ArrayView<const char>>>& data, const Float) {
+auto MagnumFont::doOpenData(const std::vector<std::pair<std::string, Containers::ArrayView<const char>>>& data, const Float) -> Metrics {
     /* We need just the configuration file and image file */
     if(data.size() != 2) {
         Error() << "Text::MagnumFont::openData(): wanted two files, got" << data.size();
@@ -112,7 +112,7 @@ std::pair<Float, Float> MagnumFont::doOpenData(const std::vector<std::pair<std::
     return openInternal(std::move(conf), std::move(*image));
 }
 
-std::pair<Float, Float> MagnumFont::doOpenFile(const std::string& filename, Float) {
+auto MagnumFont::doOpenFile(const std::string& filename, Float) -> Metrics {
     /* Open the configuration file */
     Utility::Configuration conf(filename, Utility::Configuration::Flag::ReadOnly|Utility::Configuration::Flag::SkipComments);
     if(!conf.isValid() || conf.isEmpty()) {
@@ -143,7 +143,7 @@ std::pair<Float, Float> MagnumFont::doOpenFile(const std::string& filename, Floa
     return openInternal(std::move(conf), std::move(*image));
 }
 
-std::pair<Float, Float> MagnumFont::openInternal(Utility::Configuration&& conf, Trade::ImageData2D&& image) {
+auto MagnumFont::openInternal(Utility::Configuration&& conf, Trade::ImageData2D&& image) -> Metrics {
     /* Everything okay, save the data internally */
     _opened = new Data{std::move(conf), std::move(image), std::unordered_map<char32_t, UnsignedInt>{}, {}};
 
@@ -161,7 +161,10 @@ std::pair<Float, Float> MagnumFont::openInternal(Utility::Configuration&& conf,
         _opened->glyphId.emplace(c->value<char32_t>("unicode"), glyphId);
     }
 
-    return {_opened->conf.value<Float>("fontSize"), _opened->conf.value<Float>("lineHeight")};
+    return {_opened->conf.value<Float>("fontSize"),
+            _opened->conf.value<Float>("ascent"),
+            _opened->conf.value<Float>("descent"),
+            _opened->conf.value<Float>("lineHeight")};
 }
 
 void MagnumFont::doClose() {

src/MagnumPlugins/MagnumFont/MagnumFont.h

@@ -120,9 +120,9 @@ class MagnumFont: public AbstractFont {
 
         bool doIsOpened() const override;
 
-        std::pair<Float, Float> doOpenData(const std::vector<std::pair<std::string, Containers::ArrayView<const char>>>& data, Float) override;
+        Metrics doOpenData(const std::vector<std::pair<std::string, Containers::ArrayView<const char>>>& data, Float) override;
 
-        std::pair<Float, Float> doOpenFile(const std::string& filename, Float) override;
+        Metrics doOpenFile(const std::string& filename, Float) override;
 
         void doClose() override;
 
@@ -134,7 +134,7 @@ class MagnumFont: public AbstractFont {
 
         std::unique_ptr<AbstractLayouter> doLayout(const GlyphCache& cache, Float size, const std::string& text) override;
 
-        std::pair<Float, Float> openInternal(Utility::Configuration&& conf, Trade::ImageData2D&& image);
+        Metrics openInternal(Utility::Configuration&& conf, Trade::ImageData2D&& image);
 
         Data* _opened;
 };

src/MagnumPlugins/MagnumFont/Test/MagnumFontGLTest.cpp

@@ -52,6 +52,8 @@ void MagnumFontGLTest::properties() {
     MagnumFont font;
     CORRADE_VERIFY(font.openFile(Utility::Directory::join(MAGNUMFONT_TEST_DIR, "font.conf"), 0.0f));
     CORRADE_COMPARE(font.size(), 16.0f);
+    CORRADE_COMPARE(font.ascent(), 25.0f);
+    CORRADE_COMPARE(font.descent(), -10.0f);
     CORRADE_COMPARE(font.lineHeight(), 39.7333f);
     CORRADE_COMPARE(font.glyphAdvance(font.glyphId(U'W')), Vector2(23.0f, 0.0f));
 }

src/MagnumPlugins/MagnumFont/Test/font.conf

@@ -3,6 +3,8 @@ image=font.tga
 originalImageSize=1536 1536
 padding=24 24
 fontSize=16
+ascent=25
+descent=-10
 lineHeight=39.7333
 [char]
 unicode=57

src/MagnumPlugins/MagnumFont/pluginRegistration.cpp

@@ -26,4 +26,4 @@
 #include "MagnumPlugins/MagnumFont/MagnumFont.h"
 
 CORRADE_PLUGIN_REGISTER(MagnumFont, Magnum::Text::MagnumFont,
-    "cz.mosra.magnum.Text.AbstractFont/0.2.3")
+    "cz.mosra.magnum.Text.AbstractFont/0.2.4")

src/MagnumPlugins/MagnumFontConverter/MagnumFontConverter.cpp

@@ -53,6 +53,8 @@ std::vector<std::pair<std::string, Containers::Array<char>>> MagnumFontConverter
     configuration.setValue("originalImageSize", cache.textureSize());
     configuration.setValue("padding", cache.padding());
     configuration.setValue("fontSize", font.size());
+    configuration.setValue("ascent", font.ascent());
+    configuration.setValue("descent", font.descent());
     configuration.setValue("lineHeight", font.lineHeight());
 
     /* Compress glyph IDs so the glyphs are in consecutive array, glyph 0

src/MagnumPlugins/MagnumFontConverter/Test/MagnumFontConverterGLTest.cpp

@@ -65,9 +65,9 @@ void MagnumFontConverterGLTest::exportFont() {
         private:
             void doClose() { _opened = false; }
             bool doIsOpened() const { return _opened; }
-            std::pair<Float, Float> doOpenFile(const std::string&, Float) {
+            Metrics doOpenFile(const std::string&, Float) {
                 _opened = true;
-                return {16.0f, 39.7333f};
+                return {16.0f, 25.0f, -10.0f, 39.7333f};
             }
             Features doFeatures() const { return {}; }
             std::unique_ptr<AbstractLayouter> doLayout(const GlyphCache&, Float, const std::string&) { return nullptr; }

src/MagnumPlugins/MagnumFontConverter/pluginRegistration.cpp

@@ -26,4 +26,4 @@
 #include "MagnumPlugins/MagnumFontConverter/MagnumFontConverter.h"
 
 CORRADE_PLUGIN_REGISTER(MagnumFontConverter, Magnum::Text::MagnumFontConverter,
-    "cz.mosra.magnum.Text.AbstractFontConverter/0.1.1")
+    "cz.mosra.magnum.Text.AbstractFontConverter/0.1.2")