From a2260f31fbef3da69a9039b66da30a68eece2056 Mon Sep 17 00:00:00 2001
From: Gabriel Studer <gabriel.studer@unibas.ch>
Date: Wed, 21 Oct 2020 15:38:27 +0200
Subject: [PATCH] fix OpenGL artefacts at scene export
When exporting the scene for the second time, weird artefacts that looked
like shadows occured. The fix enforces to re-allocate the resources of
the offscreen QOpenGLContext. Measurements showed that reallocation is
much faster than the rate-limiting step of the Export function: dump the
file to disk. Performance impact is therefore limited. Feel free to
investigate and propose a more elegant fix...
---
modules/gui/src/gl_canvas.cc | 31 ++++++++++++++++---------------
1 file changed, 16 insertions(+), 15 deletions(-)
diff --git a/modules/gui/src/gl_canvas.cc b/modules/gui/src/gl_canvas.cc
index 1dfdbdb7d..da2eb2816 100644
--- a/modules/gui/src/gl_canvas.cc
+++ b/modules/gui/src/gl_canvas.cc
@@ -241,7 +241,6 @@ void GLCanvas::Export(const String& fname, unsigned int width,
// setup of context, surface, fbo etc are implemented as in the QT
// threadrenderer example
-
gfx::Viewport old_vp = gfx::Scene::Instance().GetViewport();
if(old_vp.width == static_cast<int>(width) &&
@@ -253,34 +252,36 @@ void GLCanvas::Export(const String& fname, unsigned int width,
offscreen_flag_ = true;
- if(offscreen_surface_ == NULL) {
- offscreen_surface_ = new QOffscreenSurface();
- QSurfaceFormat f = this->context()->format();
- if(max_samples > 0) {
- f.setSamples(max_samples);
- }
- offscreen_surface_->setFormat(f);
- offscreen_surface_->create();
- }
-
- if(offscreen_context_ == NULL) {
- QOpenGLContext *current = this->context();
+ if(offscreen_context_ == NULL || offscreen_surface_ == NULL) {
// Some GL implementations require that the currently bound context is
// made non-current before we set up sharing, so we doneCurrent here
// and makeCurrent down below while setting up our own context.
- current->doneCurrent();
+ this->context()->doneCurrent();
offscreen_context_ = new QOpenGLContext();
QSurfaceFormat f = this->context()->format();
if(max_samples > 0) {
f.setSamples(max_samples);
}
offscreen_context_->setFormat(f);
- offscreen_context_->setShareContext(current);
+ offscreen_context_->setShareContext(this->context());
offscreen_context_->create();
+
+ offscreen_surface_ = new QOffscreenSurface();
+ offscreen_surface_->setFormat(offscreen_context_->format());
+ offscreen_surface_->create();
+
offscreen_context_->makeCurrent(offscreen_surface_);
gfx::Scene::Instance().ContextSwitch();
gfx::Scene::Instance().InitGL(false);
} else {
+ this->context()->doneCurrent();
+ // The following line destroys and recreates the existing OpenGL context.
+ // This is an ugly fix to avoid weird artefacts when calling the Export
+ // function the second time. On a low-end Laptop this requires ~5-10ms and
+ // is therefore much faster than the rate-limiting saving of the image to
+ // disk at the end of the function. Feel free to investigate and propose a
+ // more efficient solution.
+ offscreen_context_->create();
offscreen_context_->makeCurrent(offscreen_surface_);
gfx::Scene::Instance().ContextSwitch();
// the following InitGL sets potentially changed glClearcolor etc
--
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