Text: ported GlyphCache to older OpenGL and OpenGL ES.

* Not requiring ARB_texture_storage, as Texture::setStorage() has
   already implemented fallback.
 * Not requiring EXT_texture_rg for single-channel texture on ES2, as
   this extension might not be available everywhere (unlike in ES3
   desktop OpenGL, where Mesa 8/9 with OpenGL 2.1 supports it), fallback
   to Luminance in GlyphCache and RGB in DistanceFieldGlyphCache,
   because Luminance might not be renderable everywhere.
 * Re-enabled building of Text library in all ES PKGBUILDs.

PKGBUILD-es2

@@ -26,7 +26,6 @@ build() {
         -DBUILD_TESTS=ON \
         -DTARGET_GLES=ON \
         -DTARGET_GLES2=ON \
-        -DWITH_TEXT=OFF \
         -DWITH_MAGNUMINFO=OFF \
         -DWITH_XEGLAPPLICATION=ON
     make

PKGBUILD-es2desktop

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

PKGBUILD-es3

@@ -26,7 +26,6 @@ build() {
         -DBUILD_TESTS=ON \
         -DTARGET_GLES=ON \
         -DTARGET_GLES2=OFF \
-        -DWITH_TEXT=OFF \
         -DWITH_MAGNUMINFO=OFF \
         -DWITH_XEGLAPPLICATION=ON
     make

src/Text/DistanceFieldGlyphCache.cpp

@@ -26,30 +26,54 @@
 
 #include "Extensions.h"
 #include "Image.h"
+#ifndef CORRADE_NO_ASSERT
+#include "ImageFormat.h"
+#endif
 #include "TextureFormat.h"
 #include "TextureTools/DistanceField.h"
 
 namespace Magnum { namespace Text {
 
-namespace {
+DistanceFieldGlyphCache::DistanceFieldGlyphCache(const Vector2i& originalSize, const Vector2i& distanceFieldSize, UnsignedInt radius): GlyphCache(originalSize, Vector2i(radius)), scale(Vector2(distanceFieldSize)/originalSize), radius(radius) {
+    #ifndef MAGNUM_TARGET_GLES
+    MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::ARB::texture_rg);
+    #endif
+
     #if !defined(MAGNUM_TARGET_GLES) || defined(MAGNUM_TARGET_GLES3)
     const TextureFormat internalFormat = TextureFormat::R8;
     #else
-    const TextureFormat internalFormat = TextureFormat::Red;
+    const TextureFormat internalFormat =
+        Context::current()->isExtensionSupported<Extensions::GL::EXT::texture_rg>() ?
+        TextureFormat::Red : TextureFormat::RGB;
+    if(internalFormat == TextureFormat::RGB)
+        Warning() << "Text::DistanceFieldGlyphCache:" << Extensions::GL::EXT::texture_rg::string() << "not supported, using inefficient RGB format for glyph cache texture";
     #endif
+
+    initialize(internalFormat, distanceFieldSize);
 }
 
-DistanceFieldGlyphCache::DistanceFieldGlyphCache(const Vector2i& originalSize, const Vector2i& distanceFieldSize, UnsignedInt radius): GlyphCache(originalSize, Vector2i(radius)), scale(Vector2(distanceFieldSize)/originalSize), radius(radius) {
+void DistanceFieldGlyphCache::setImage(const Vector2i& offset, Image2D* const image) {
     #ifndef MAGNUM_TARGET_GLES
     MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::ARB::texture_rg);
-    #else
-    MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::EXT::texture_rg);
     #endif
 
-    initialize(internalFormat, distanceFieldSize);
+    #if !defined(MAGNUM_TARGET_GLES) || defined(MAGNUM_TARGET_GLES3)
-}
+    const TextureFormat internalFormat = TextureFormat::R8;
+    CORRADE_ASSERT(image->format() == ImageFormat::Red,
+        "Text::DistanceFieldGlyphCache::setImage(): expected" << ImageFormat::Red << "but got" << image->format(), );
+    #else
+    TextureFormat internalFormat;
+    if(Context::current()->isExtensionSupported<Extensions::GL::EXT::texture_rg>()) {
+        internalFormat = TextureFormat::Red;
+        CORRADE_ASSERT(image->format() == ImageFormat::Red,
+            "Text::DistanceFieldGlyphCache::setImage(): expected" << ImageFormat::Red << "but got" << image->format(), );
+    } else {
+        internalFormat = TextureFormat::Luminance;
+        CORRADE_ASSERT(image->format() == ImageFormat::Luminance,
+            "Text::DistanceFieldGlyphCache::setImage(): expected" << ImageFormat::Luminance << "but got" << image->format(), );
+    }
+    #endif
 
-void DistanceFieldGlyphCache::setImage(const Vector2i& offset, Image2D* const image) {
     Texture2D input;
     input.setWrapping(Sampler::Wrapping::ClampToEdge)
         ->setMinificationFilter(Sampler::Filter::Linear)

src/Text/DistanceFieldGlyphCache.h

@@ -62,7 +62,10 @@ class MAGNUM_TEXT_EXPORT DistanceFieldGlyphCache: public GlyphCache {
          * @param radius            Distance field computation radius
          *
          * See TextureTools::distanceField() for more information about the
-         * parameters.
+         * parameters. Sets internal texture format to red channel only. On
+         * desktop OpenGL requires @extension{ARB,texture_rg} (also part of
+         * OpenGL ES 3.0), in ES2 uses @es_extension{EXT,texture_rg} if
+         * available or @ref TextureFormat "TextureFormat::RGB" as fallback.
          */
         explicit DistanceFieldGlyphCache(const Vector2i& originalSize, const Vector2i& distanceFieldSize, UnsignedInt radius);
 

src/Text/GlyphCache.cpp

@@ -31,19 +31,17 @@
 
 namespace Magnum { namespace Text {
 
-namespace {
-    #if !defined(MAGNUM_TARGET_GLES) || defined(MAGNUM_TARGET_GLES3)
-    const TextureFormat internalFormat = TextureFormat::R8;
-    #else
-    const TextureFormat internalFormat = TextureFormat::Red;
-    #endif
-}
-
 GlyphCache::GlyphCache(const Vector2i& size): _size(size) {
     #ifndef MAGNUM_TARGET_GLES
     MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::ARB::texture_rg);
+    #endif
+
+    #if !defined(MAGNUM_TARGET_GLES) || defined(MAGNUM_TARGET_GLES3)
+    const TextureFormat internalFormat = TextureFormat::R8;
     #else
-    MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::EXT::texture_rg);
+    const TextureFormat internalFormat =
+        Context::current()->isExtensionSupported<Extensions::GL::EXT::texture_rg>() ?
+        TextureFormat::Red : TextureFormat::Luminance;
     #endif
 
     initialize(internalFormat, size);
@@ -59,12 +57,6 @@ GlyphCache::~GlyphCache() = default;
 
 /** @todo Delegating constructor when support for GCC 4.6 is dropped */
 void GlyphCache::initialize(const TextureFormat internalFormat, const Vector2i& size) {
-    #ifndef MAGNUM_TARGET_GLES
-    MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::ARB::texture_storage);
-    #else
-    MAGNUM_ASSERT_EXTENSION_SUPPORTED(Extensions::GL::EXT::texture_storage);
-    #endif
-
     _texture.setWrapping(Sampler::Wrapping::ClampToEdge)
         ->setMinificationFilter(Sampler::Filter::Linear)
         ->setMagnificationFilter(Sampler::Filter::Linear)

src/Text/GlyphCache.h

@@ -69,9 +69,10 @@ class MAGNUM_TEXT_EXPORT GlyphCache {
          * @brief Constructor
          * @param size              Glyph cache texture size
          *
-         * Sets internal texture format to red channel only. Requires
+         * Sets internal texture format to red channel only. On desktop OpenGL
-         * @extension{ARB,texture_rg} (also part of OpenGL ES 3.0 or available
+         * requires @extension{ARB,texture_rg} (also part of OpenGL ES 3.0), in
-         * as @es_extension{EXT,texture_rg} in ES 2.0).
+         * ES2 uses @es_extension{EXT,texture_rg}, if available, or
+         * @ref TextureFormat "TextureFormat::Luminance" as fallback.
          */
         explicit GlyphCache(const Vector2i& size);