TextureTools: add a DistanceField overload taking a framebuffer.

So one can directly read it back on GLES without having to wrap the
texture in a framebuffer again.

This change also puts the framebuffer completeness check *before* the
clear() and bind() which makes it no longer emit a GL error. The error
is still silent though, which isn't nice. Gotta fix that eventually as
well.

doc/changelog.dox

@@ -329,6 +329,9 @@ See also:
 
 -   New @ref TextureTools::atlasArrayPowerOfTwo() utility for optimal packing
     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
 
 @subsubsection changelog-latest-new-trade Trade library
 

src/Magnum/TextureTools/DistanceField.cpp

@@ -189,7 +189,7 @@ DistanceField::~DistanceField() = default;
 
 UnsignedInt DistanceField::radius() const { return _state->radius; }
 
-void DistanceField::operator()(GL::Texture2D& input, GL::Texture2D& output, const Range2Di& rectangle, const Vector2i&
+void DistanceField::operator()(GL::Texture2D& input, GL::Framebuffer& output, const Range2Di& rectangle, const Vector2i&
     #ifdef MAGNUM_TARGET_GLES
     imageSize
     #endif
@@ -200,20 +200,17 @@ void DistanceField::operator()(GL::Texture2D& input, GL::Texture2D& output, cons
     Vector2i imageSize = input.imageSize(0);
     #endif
 
-    /* Framebuffer is instantiated here so it gets correctly unbound at the end
+    const GL::Framebuffer::Status status = output.checkStatus(GL::FramebufferTarget::Draw);
-       (and bound framebuffer reset back to the default) */
-    GL::Framebuffer framebuffer{rectangle};
-    framebuffer.attachTexture(GL::Framebuffer::ColorAttachment(0), output, 0)
-        .clear(GL::FramebufferClear::Color)
-        .bind();
-
-    const GL::Framebuffer::Status status = framebuffer.checkStatus(GL::FramebufferTarget::Draw);
     if(status != GL::Framebuffer::Status::Complete) {
         Error() << "TextureTools::DistanceField: cannot render to given output texture, unexpected framebuffer status"
                 << status;
         return;
     }
 
+    output
+        .clear(GL::FramebufferClear::Color)
+        .bind();
+
     _state->shader.setScaling(Vector2(imageSize)/Vector2(rectangle.size()))
         .bindTexture(input);
 
@@ -230,4 +227,19 @@ void DistanceField::operator()(GL::Texture2D& input, GL::Texture2D& output, cons
     _state->shader.draw(_state->mesh);
 }
 
+void DistanceField::operator()(GL::Texture2D& input, GL::Texture2D& output, const Range2Di& rectangle, const Vector2i&
+    #ifdef MAGNUM_TARGET_GLES
+    imageSize
+    #endif
+) {
+    GL::Framebuffer framebuffer{rectangle};
+    framebuffer.attachTexture(GL::Framebuffer::ColorAttachment(0), output, 0);
+
+    operator()(input, framebuffer, rectangle
+        #ifdef MAGNUM_TARGET_GLES
+        , imageSize
+        #endif
+        );
+}
+
 }}

src/Magnum/TextureTools/DistanceField.h

@@ -110,13 +110,32 @@ class MAGNUM_TEXTURETOOLS_EXPORT DistanceField {
         UnsignedInt radius() const;
 
         /**
-         * @brief Calculate the distance field
+         * @brief Calculate the distance field to a framebuffer
+         * @param input        Input texture
+         * @param output       Output framebuffer
+         * @param rectangle    Rectangle in output texture where to render
+         * @param imageSize    Input texture size. Needed only for OpenGL ES,
+         *      on desktop GL the information is gathered automatically using
+         *      @ref GL::Texture2D::imageSize().
+         * @m_since_latest
+         */
+        void operator()(GL::Texture2D& input, GL::Framebuffer& output, const Range2Di& rectangle, const Vector2i& imageSize
+            #ifndef MAGNUM_TARGET_GLES
+            = {}
+            #endif
+        );
+
+        /**
+         * @brief Calculate the distance field to a texture
          * @param input        Input texture
          * @param output       Output texture
          * @param rectangle    Rectangle in output texture where to render
          * @param imageSize    Input texture size. Needed only for OpenGL ES,
          *      on desktop GL the information is gathered automatically using
          *      @ref GL::Texture2D::imageSize().
+         *
+         * Creates a framebuffer with @p output attached and calls
+         * @ref operator()(GL::Texture2D&, GL::Framebuffer&, const Range2Di&, const Vector2i&).
          */
         void operator()(GL::Texture2D& input, GL::Texture2D& output, const Range2Di& rectangle, const Vector2i& imageSize
             #ifndef MAGNUM_TARGET_GLES

src/Magnum/TextureTools/Test/DistanceFieldGLTest.cpp

@@ -23,9 +23,11 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+#include <sstream>
 #include <Corrade/Containers/String.h>
 #include <Corrade/PluginManager/AbstractManager.h>
 #include <Corrade/Utility/Path.h>
+#include <Corrade/Utility/DebugStl.h>
 
 #ifdef CORRADE_TARGET_APPLE
 #include <Corrade/Containers/Pair.h>
@@ -64,6 +66,8 @@ namespace Magnum { namespace TextureTools { namespace Test { namespace {
 struct DistanceFieldGLTest: GL::OpenGLTester {
     explicit DistanceFieldGLTest();
 
+    /* This tests the GL::Texture overload, which itself calls into the
+       GL::Framebuffer overload so both are covered */
     void test();
     #ifndef MAGNUM_TARGET_WEBGL
     void benchmark();
@@ -170,24 +174,28 @@ void DistanceFieldGLTest::test() {
 
     MAGNUM_VERIFY_NO_GL_ERROR();
 
-    distanceField(input, output, {{}, Vector2i{64}}
+    std::ostringstream out;
-        #ifdef MAGNUM_TARGET_GLES
+    {
-        , inputImage->size()
+        Error redirectError{&out};
-        #endif
+        distanceField(input, output, {{}, Vector2i{64}}
-        );
+            #ifdef MAGNUM_TARGET_GLES
+            , inputImage->size()
+            #endif
+            );
+    }
 
     #ifdef MAGNUM_TARGET_GLES
+    /* Probably due to the luminance target pixel format? Works with 4.1,
+        didn't find any commit in between that would clearly affect
+        this. */
+    if(GL::Context::current().versionString().contains("SwiftShader 4.0.0"_s)) {
+        CORRADE_COMPARE(out.str(), "TextureTools::DistanceField: cannot render to given output texture, unexpected framebuffer status GL::Framebuffer::Status::IncompleteAttachment\n");
+        CORRADE_SKIP("SwiftShader 4.0.0 has a bug where the framebuffer is considered incomplete.");
+    } else
+    #endif
     {
-        /* Probably due to the luminance target pixel format? Works with 4.1,
+        CORRADE_COMPARE(out.str(), "");
-           didn't find any commit in between that would clearly affect
-           this. */
-        CORRADE_EXPECT_FAIL_IF(GL::Context::current().versionString().contains("SwiftShader 4.0.0"_s),
-            "SwiftShader 4.0.0 has a bug where the framebuffer is considered incomplete.");
-        MAGNUM_VERIFY_NO_GL_ERROR();
-        if(GL::Context::current().versionString().contains("SwiftShader 4.0.0"_s))
-            CORRADE_SKIP("Skipping the rest of the test.");
     }
-    #endif
 
     Containers::Optional<Image2D> actualOutputImage;
     #ifndef MAGNUM_TARGET_GLES2