Support MRT in QOpenGLFramebufferObject

Introduce overloads in the API to allow specifying multiple color
attachment sizes and formats. When these are in use and MRT is supported,
a texture or renderbuffer is created for each of GL_COLOR_ATTACHMENT0, 1, 2, ...

[ChangeLog] Added support for multiple render targets in QOpenGLFramebufferObject

Task-number: QTBUG-39235
Change-Id: Ie7cfd81d1b796a9166b80dff7513aafe0120d53d
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/src/gui/opengl/qopenglfunctions.cpp b/src/gui/opengl/qopenglfunctions.cpp
index 8f3959189d..668eaa9a89 100644
--- a/src/gui/opengl/qopenglfunctions.cpp
+++ b/src/gui/opengl/qopenglfunctions.cpp
@@ -184,6 +184,7 @@ Q_LOGGING_CATEGORY(lcGLES3, "qt.opengl.es3")
     \value NPOTTextureRepeat Non power of two textures can use GL_REPEAT as wrap parameter.
     \value FixedFunctionPipeline The fixed function pipeline is available.
     \value TextureRGFormats The GL_RED and GL_RG texture formats are available.
+    \value MultipleRenderTargets Multiple color attachments to framebuffer objects are available.
 */
 
 // Hidden private fields for additional extension data.
@@ -275,7 +276,7 @@ static int qt_gl_resolve_features()
 {
     QOpenGLContext *ctx = QOpenGLContext::currentContext();
     if (ctx->isOpenGLES()) {
-        // OpenGL ES 2
+        // OpenGL ES
         int features = QOpenGLFunctions::Multitexture |
             QOpenGLFunctions::Shaders |
             QOpenGLFunctions::Buffers |
@@ -300,6 +301,8 @@ static int qt_gl_resolve_features()
             if (!(renderer && strstr(renderer, "Mesa")))
                 features |= QOpenGLFunctions::TextureRGFormats;
         }
+        if (ctx->format().majorVersion() >= 3)
+            features |= QOpenGLFunctions::MultipleRenderTargets;
         return features;
     } else {
         // OpenGL
@@ -308,10 +311,9 @@ static int qt_gl_resolve_features()
         QOpenGLExtensionMatcher extensions;
 
         if (format.majorVersion() >= 3)
-            features |= QOpenGLFunctions::Framebuffers;
-        else if (extensions.match("GL_EXT_framebuffer_object") ||
-                extensions.match("GL_ARB_framebuffer_object"))
-                features |= QOpenGLFunctions::Framebuffers;
+            features |= QOpenGLFunctions::Framebuffers | QOpenGLFunctions::MultipleRenderTargets;
+        else if (extensions.match("GL_EXT_framebuffer_object") || extensions.match("GL_ARB_framebuffer_object"))
+            features |= QOpenGLFunctions::Framebuffers | QOpenGLFunctions::MultipleRenderTargets;
 
         if (format.majorVersion() >= 2) {
             features |= QOpenGLFunctions::BlendColor |