Reuse any binding (not just draw) when adding framebuffer attachments.

src/AbstractFramebuffer.cpp

@@ -57,6 +57,25 @@ void AbstractFramebuffer::bindInternal(Target target) {
 
     glBindFramebuffer(static_cast<GLenum>(target), _id);
 }
+
+AbstractFramebuffer::Target AbstractFramebuffer::bindInternal() {
+    Implementation::FramebufferState* state = Context::current()->state()->framebuffer;
+
+    /* Return target to which the framebuffer is already bound */
+    if(state->readBinding == _id && state->drawBinding == _id)
+        return Target::ReadDraw;
+    if(state->readBinding == _id)
+        return Target::Read;
+    if(state->drawBinding == _id)
+        return Target::Draw;
+
+    /* Or bind it, if not already */
+    state->readBinding = _id;
+    if(readTarget == Target::ReadDraw) state->drawBinding = _id;
+
+    glBindFramebuffer(GLenum(readTarget), _id);
+    return readTarget;
+}
 #endif
 
 void AbstractFramebuffer::blit(AbstractFramebuffer& source, AbstractFramebuffer& destination, const Vector2i& sourceBottomLeft, const Vector2i& sourceTopRight, const Vector2i& destinationBottomLeft, const Vector2i& destinationTopRight, AbstractFramebuffer::BlitMask mask, AbstractFramebuffer::BlitFilter filter) {

src/AbstractFramebuffer.h

@@ -253,6 +253,7 @@ class MAGNUM_EXPORT AbstractFramebuffer {
     #ifndef DOXYGEN_GENERATING_OUTPUT
     protected:
         void MAGNUM_LOCAL bindInternal(Target target);
+        Target MAGNUM_LOCAL bindInternal();
         void MAGNUM_LOCAL setViewportInternal();
 
         static MAGNUM_LOCAL Target readTarget;

src/Framebuffer.cpp

@@ -92,8 +92,7 @@ void Framebuffer::initializeContextBasedFunctionality(Context* context) {
 }
 
 void Framebuffer::renderbufferImplementationDefault(GLenum attachment, Renderbuffer* renderbuffer) {
-    bindInternal(drawTarget);
-    glFramebufferRenderbuffer(static_cast<GLenum>(drawTarget), attachment, GL_RENDERBUFFER, renderbuffer->id());
+    glFramebufferRenderbuffer(GLenum(bindInternal()), attachment, GL_RENDERBUFFER, renderbuffer->id());
 }
 
 #ifndef MAGNUM_TARGET_GLES
@@ -102,8 +101,7 @@ void Framebuffer::renderbufferImplementationDSA(GLenum attachment, Renderbuffer*
 }
 
 void Framebuffer::texture1DImplementationDefault(GLenum attachment, Texture1D* texture, GLint mipLevel) {
-    bindInternal(drawTarget);
-    glFramebufferTexture1D(static_cast<GLenum>(drawTarget), attachment, static_cast<GLenum>(texture->target()), texture->id(), mipLevel);
+    glFramebufferTexture1D(GLenum(bindInternal()), attachment, static_cast<GLenum>(texture->target()), texture->id(), mipLevel);
 }
 
 void Framebuffer::texture1DImplementationDSA(GLenum attachment, Texture1D* texture, GLint mipLevel) {
@@ -112,8 +110,7 @@ void Framebuffer::texture1DImplementationDSA(GLenum attachment, Texture1D* textu
 #endif
 
 void Framebuffer::texture2DImplementationDefault(GLenum attachment, GLenum textureTarget, GLuint textureId, GLint mipLevel) {
-    bindInternal(drawTarget);
-    glFramebufferTexture2D(static_cast<GLenum>(drawTarget), attachment, textureTarget, textureId, mipLevel);
+    glFramebufferTexture2D(GLenum(bindInternal()), attachment, textureTarget, textureId, mipLevel);
 }
 
 #ifndef MAGNUM_TARGET_GLES
@@ -124,10 +121,9 @@ void Framebuffer::texture2DImplementationDSA(GLenum attachment, GLenum textureTa
 
 void Framebuffer::texture3DImplementationDefault(GLenum attachment, Texture3D* texture, GLint mipLevel, GLint layer) {
     /** @todo Check for texture target compatibility */
-    bindInternal(drawTarget);
     /** @todo Get some extension wrangler for glFramebufferTexture3D() (extension only) */
     #ifndef MAGNUM_TARGET_GLES
-    glFramebufferTexture3D(static_cast<GLenum>(drawTarget), attachment, static_cast<GLenum>(texture->target()), texture->id(), mipLevel, layer);
+    glFramebufferTexture3D(GLenum(bindInternal()), attachment, static_cast<GLenum>(texture->target()), texture->id(), mipLevel, layer);
     #else
     static_cast<void>(attachment);
     static_cast<void>(texture);