distancefieldconverter: make it work on GLES 3+.

It compiles on GLES2 as well, but there it hits the massive PITA of
being unable to render to LUMINANXCE formats and GL_RED formats not
really being available everywhere.

I don't have the patience to fix that, and almost nobody needs to use
ES2 platforms nowadays, so this isn't really a priority.

doc/changelog.dox

@@ -331,7 +331,9 @@ See also:
     of power-of-two textures into a texture atlas array
 -   Added a @ref TextureTools::DistanceField::operator()() overload taking a
     @ref GL::Framebuffer instead of a @ref GL::Texture as an output for an
-    easier ability to download the resulting image on OpenGL ES platforms
+    easier ability to download the resulting image on OpenGL ES platforms;
+    the @ref magnum-distancefieldconverter "magnum-distancefieldconverter"
+    utility thus now compiles works and on OpenGL ES 3+ as well
 
 @subsubsection changelog-latest-new-trade Trade library
 

package/archlinux/PKGBUILD-es2

@@ -39,6 +39,7 @@ build() {
         -DMAGNUM_WITH_TGAIMAGECONVERTER=ON \
         -DMAGNUM_WITH_TGAIMPORTER=ON \
         -DMAGNUM_WITH_WAVAUDIOIMPORTER=ON \
+        -DMAGNUM_WITH_DISTANCEFIELDCONVERTER=OFF \
         -DMAGNUM_WITH_IMAGECONVERTER=ON \
         -DMAGNUM_WITH_SCENECONVERTER=ON \
         -DMAGNUM_WITH_SHADERCONVERTER=ON \

package/archlinux/PKGBUILD-es2desktop

@@ -43,6 +43,7 @@ build() {
         -DMAGNUM_WITH_TGAIMAGECONVERTER=ON \
         -DMAGNUM_WITH_TGAIMPORTER=ON \
         -DMAGNUM_WITH_WAVAUDIOIMPORTER=ON \
+        -DMAGNUM_WITH_DISTANCEFIELDCONVERTER=OFF \
         -DMAGNUM_WITH_IMAGECONVERTER=ON \
         -DMAGNUM_WITH_SCENECONVERTER=ON \
         -DMAGNUM_WITH_SHADERCONVERTER=ON \

package/archlinux/PKGBUILD-es3

@@ -39,6 +39,7 @@ build() {
         -DMAGNUM_WITH_TGAIMAGECONVERTER=ON \
         -DMAGNUM_WITH_TGAIMPORTER=ON \
         -DMAGNUM_WITH_WAVAUDIOIMPORTER=ON \
+        -DMAGNUM_WITH_DISTANCEFIELDCONVERTER=ON \
         -DMAGNUM_WITH_IMAGECONVERTER=ON \
         -DMAGNUM_WITH_SCENECONVERTER=ON \
         -DMAGNUM_WITH_SHADERCONVERTER=ON \

package/archlinux/PKGBUILD-es3desktop

@@ -43,6 +43,7 @@ build() {
         -DMAGNUM_WITH_TGAIMAGECONVERTER=ON \
         -DMAGNUM_WITH_TGAIMPORTER=ON \
         -DMAGNUM_WITH_WAVAUDIOIMPORTER=ON \
+        -DMAGNUM_WITH_DISTANCEFIELDCONVERTER=ON \
         -DMAGNUM_WITH_IMAGECONVERTER=ON \
         -DMAGNUM_WITH_SCENECONVERTER=ON \
         -DMAGNUM_WITH_SHADERCONVERTER=ON \

package/ci/appveyor-desktop-gles.bat

@@ -49,7 +49,7 @@ cmake .. ^
     -DMAGNUM_WITH_TGAIMAGECONVERTER=ON ^
     -DMAGNUM_WITH_TGAIMPORTER=ON ^
     -DMAGNUM_WITH_WAVAUDIOIMPORTER=OFF ^
-    -DMAGNUM_WITH_DISTANCEFIELDCONVERTER=OFF ^
+    -DMAGNUM_WITH_DISTANCEFIELDCONVERTER=%TARGET_GLES3% ^
     -DMAGNUM_WITH_FONTCONVERTER=OFF ^
     -DMAGNUM_WITH_IMAGECONVERTER=OFF ^
     -DMAGNUM_WITH_SCENECONVERTER=OFF ^

package/ci/appveyor.yml

@@ -122,6 +122,8 @@ install:
 - set PATH=C:/tools/ninja;%PATH%
 - IF "%TARGET%" == "desktop" IF "%COMPILER%" == "mingw" pip install codecov
 
+- IF "%TARGET_GLES2%" == "ON" set TARGET_GLES3=OFF
+- IF "%TARGET_GLES2%" == "OFF" set TARGET_GLES3=ON
 - IF NOT "%BUILD_STATIC%" == "ON" set BUILD_STATIC=OFF
 # For ES builds, otherwise the "%COMPILER:~0,4%" below doesn't work, sigh
 - IF "%COMPILER%" == "" set COMPILER=msvc

package/ci/circleci.yml

@@ -246,6 +246,8 @@ commands:
           if [ "$BUILD_STATIC" != "ON" ]; then export BUILD_STATIC=OFF; fi
           if [ "$BUILD_DEPRECATED" != "OFF" ]; then export BUILD_DEPRECATED=ON; fi
           if [ "$BUILD_APPLICATIONS" != "OFF" ]; then export BUILD_APPLICATIONS=ON; fi
+          if [ "$TARGET_GLES2" == "ON" ]; then export TARGET_GLES3=OFF; fi
+          if [ "$TARGET_GLES2" == "OFF" ]; then export TARGET_GLES3=ON; fi
           ./package/ci/<< parameters.script >>
 
   lcov:

package/ci/unix-desktop-gles.sh

@@ -48,7 +48,7 @@ cmake .. \
     -DMAGNUM_WITH_TGAIMAGECONVERTER=ON \
     -DMAGNUM_WITH_TGAIMPORTER=ON \
     -DMAGNUM_WITH_WAVAUDIOIMPORTER=OFF \
-    -DMAGNUM_WITH_DISTANCEFIELDCONVERTER=OFF \
+    -DMAGNUM_WITH_DISTANCEFIELDCONVERTER=$TARGET_GLES3 \
     -DMAGNUM_WITH_FONTCONVERTER=OFF \
     -DMAGNUM_WITH_IMAGECONVERTER=OFF \
     -DMAGNUM_WITH_SCENECONVERTER=OFF \

src/Magnum/TextureTools/distancefieldconverter.cpp

@@ -35,6 +35,7 @@
 #include "Magnum/PixelFormat.h"
 #include "Magnum/Math/ConfigurationValue.h"
 #include "Magnum/Math/Range.h"
+#include "Magnum/GL/Framebuffer.h"
 #include "Magnum/GL/Renderer.h"
 #include "Magnum/GL/Texture.h"
 #include "Magnum/GL/TextureFormat.h"
@@ -176,6 +177,10 @@ int DistanceFieldConverter::exec() {
     }
 
     /* Decide about internal format */
+    /** @todo this doesn't work on ES2, the image pixel format is converted to
+        a LUMINANCE which doesn't match GL_RED / GL_R8; it also doesn't check
+        that EXT_texture_rg exists, and LUMINANCE isn't really renderable, etc
+        etc */
     GL::TextureFormat internalFormat;
     if(image->format() == PixelFormat::R8Unorm)
         internalFormat = GL::TextureFormat::R8;
@@ -200,15 +205,22 @@ int DistanceFieldConverter::exec() {
     GL::Texture2D output;
     output.setStorage(1, GL::TextureFormat::R8, args.value<Vector2i>("output-size"));
 
+    /* Rectangle to process */
+    const Range2Di rectangle{{}, args.value<Vector2i>("output-size")};
+
+    /* Output framebuffer */
+    GL::Framebuffer framebuffer{rectangle};
+    framebuffer.attachTexture(GL::Framebuffer::ColorAttachment(0), output, 0);
+
     CORRADE_INTERNAL_ASSERT(GL::Renderer::error() == GL::Renderer::Error::NoError);
 
     /* Do it */
     Debug() << "Converting image of size" << image->size() << "to distance field...";
-    TextureTools::DistanceField{args.value<UnsignedInt>("radius")}(input, output, {{}, args.value<Vector2i>("output-size")}, image->size());
+    TextureTools::DistanceField{args.value<UnsignedInt>("radius")}(input, output, rectangle, image->size());
 
     /* Save image */
     Image2D result{PixelFormat::R8Unorm};
-    output.image(0, result);
+    framebuffer.read(rectangle, result);
     if(!converter->convertToFile(result, args.value("output"))) {
         Error() << "Cannot save file" << args.value("output");
         return 5;