File 0001-Allow-compilation-on-GLES-platforms.patch of Package vtk

From 5c4e4e5832613e758b7c1389a5dbcc1d57db7c6e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20Br=C3=BCns?= <stefan.bruens@rwth-aachen.de>
Date: Tue, 9 Jun 2020 17:11:12 +0200
Subject: [PATCH] Allow compilation on GLES platforms

On GLES 2.0 platforms (more specifically, for Qt5 "opengl es2" builds),
QOpenGLFunctions_3_2_Core does not exist. Since Qt 5.7,
QOpenGlFramebufferObject has a static wrapper method for framebuffer
blitting, which in worst case (i.e. no GL_EXT_framebuffer blit
extension) is a noop, but handles all GL platform differences otherwise
(3.2 Core context, GLES 3.0, or any earlier with required extensions).

The code ignores the passed in targetId FBO handle, but relies on
the default framebuffer object of the context. As the calling code calls
QOpenGLWindow::makeCurrent() the context default FBO is the one returned
by QOpenGLWindow::defaultFramebufferObject().
---
 GUISupport/Qt/QVTKRenderWindowAdapter.cxx | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/GUISupport/Qt/QVTKRenderWindowAdapter.cxx b/GUISupport/Qt/QVTKRenderWindowAdapter.cxx
index 5a66e236df..e5fc5a6135 100644
--- a/GUISupport/Qt/QVTKRenderWindowAdapter.cxx
+++ b/GUISupport/Qt/QVTKRenderWindowAdapter.cxx
@@ -334,12 +334,17 @@ public:
     {
       return false;
     }
+#if QT_VERSION < QT_VERSION_CHECK(5, 7, 0)
     QOpenGLFunctions_3_2_Core* f = this->Context->versionFunctions<QOpenGLFunctions_3_2_Core>();
+#else
+    QOpenGLFunctions* f = this->Context->functions();
+#endif
     if (!f)
     {
       return false;
     }
 
+#if QT_VERSION < QT_VERSION_CHECK(5, 7, 0)
     f->glBindFramebuffer(GL_DRAW_FRAMEBUFFER, targetId);
     f->glDrawBuffer(targetAttachment);
 
@@ -358,6 +363,20 @@ public:
     auto sourceSize = this->FBO->size();
     f->glBlitFramebuffer(0, 0, sourceSize.width(), sourceSize.height(), targetRect.x(),
       targetRect.y(), targetRect.width(), targetRect.height(), GL_COLOR_BUFFER_BIT, GL_NEAREST);
+#else
+    GLboolean scissorTest = f->glIsEnabled(GL_SCISSOR_TEST);
+    if (scissorTest == GL_TRUE)
+    {
+      f->glDisable(GL_SCISSOR_TEST); // Scissor affects glBindFramebuffer.
+    }
+    auto sourceSize = this->FBO->size();
+    QRect sourceRect(0, 0, sourceSize.width(), sourceSize.height());
+    unsigned int readAttachment =
+      left ? this->RenderWindow->GetFrontLeftBuffer() : this->RenderWindow->GetFrontRightBuffer();
+    QOpenGLFramebufferObject::blitFramebuffer(nullptr, targetRect, this->FBO.get(), sourceRect,
+      GL_COLOR_BUFFER_BIT, GL_NEAREST, readAttachment, targetAttachment,
+      QOpenGLFramebufferObject::DontRestoreFramebufferBinding);
+#endif
 
     this->clearAlpha(targetRect);
 
@@ -436,7 +455,7 @@ public:
   {
     Q_ASSERT(this->Context && this->FBO);
 
-    QOpenGLFunctions_3_2_Core* f = this->Context->versionFunctions<QOpenGLFunctions_3_2_Core>();
+    QOpenGLFunctions* f = this->Context->functions();
     if (f)
     {
       // now clear alpha otherwise we end up blending the rendering with
-- 
2.27.0