Fix BlitFramebuffer on GLES

Task-number: QTBUG-68395
Change-Id: I216f32bd22d12c6fa6f2efd09765ad95754326b4
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

3 files changed, 16 insertions, 2 deletions

diff --git a/src/render/renderers/opengl/graphicshelpers/graphicscontext.cpp b/src/render/renderers/opengl/graphicshelpers/graphicscontext.cpp
index c2ec3db59..af1fb5675 100644
--- a/src/render/renderers/opengl/graphicshelpers/graphicscontext.cpp
+++ b/src/render/renderers/opengl/graphicshelpers/graphicscontext.cpp
@@ -705,6 +705,11 @@ void GraphicsContext::drawBuffer(GLenum mode)
     m_glHelper->drawBuffer(mode);
 }
 
+void GraphicsContext::drawBuffers(GLsizei n, const int *bufs)
+{
+    m_glHelper->drawBuffers(n, bufs);
+}
+
 void GraphicsContext::applyUniform(const ShaderUniform &description, const UniformValue &v)
 {
     const UniformType type = m_glHelper->uniformTypeFromGLType(description.m_type);
diff --git a/src/render/renderers/opengl/graphicshelpers/graphicscontext_p.h b/src/render/renderers/opengl/graphicshelpers/graphicscontext_p.h
index 82db57433..7bc79996c 100644
--- a/src/render/renderers/opengl/graphicshelpers/graphicscontext_p.h
+++ b/src/render/renderers/opengl/graphicshelpers/graphicscontext_p.h
@@ -158,6 +158,7 @@ public:
     void    pointSize(bool programmable, GLfloat value);
     void    readBuffer(GLenum mode);
     void    drawBuffer(GLenum mode);
+    void    drawBuffers(GLsizei n, const int *bufs);
     void    setMSAAEnabled(bool enabled);
     void    setAlphaCoverageEnabled(bool enabled);
     void    setClipPlane(int clipPlane, const QVector3D &normal, float distance);
diff --git a/src/render/renderers/opengl/graphicshelpers/submissioncontext.cpp b/src/render/renderers/opengl/graphicshelpers/submissioncontext.cpp
index ecaa12d8b..20aca81bc 100644
--- a/src/render/renderers/opengl/graphicshelpers/submissioncontext.cpp
+++ b/src/render/renderers/opengl/graphicshelpers/submissioncontext.cpp
@@ -1618,8 +1618,12 @@ void SubmissionContext::blitFramebuffer(Qt3DCore::QNodeId inputRenderTargetId,
     if (!inputBufferIsDefault)
         readBuffer(GL_COLOR_ATTACHMENT0 + inputAttachmentPoint);
 
-    if (!outputBufferIsDefault)
-        drawBuffer(GL_COLOR_ATTACHMENT0 + outputAttachmentPoint);
+    if (!outputBufferIsDefault) {
+        // Note that we use glDrawBuffers, not glDrawBuffer. The
+        // latter is not available with GLES.
+        const int buf = outputAttachmentPoint;
+        drawBuffers(1, &buf);
+    }
 
     // Blit framebuffer
     const GLenum mode = interpolationMethod ? GL_NEAREST : GL_LINEAR;
@@ -1629,6 +1633,10 @@ void SubmissionContext::blitFramebuffer(Qt3DCore::QNodeId inputRenderTargetId,
 
     // Reset draw buffer
     bindFramebuffer(lastDrawFboId, GraphicsHelperInterface::FBOReadAndDraw);
+    if (outputAttachmentPoint != QRenderTargetOutput::Color0) {
+        const int buf = QRenderTargetOutput::Color0;
+        drawBuffers(1, &buf);
+    }
 }
 
 } // namespace Render