Bugfix: Reset default framebuffer to back after rendering

Author: mbaetgen-wup

src/libprojectM/ProjectM.cpp

@@ -166,8 +166,14 @@ void ProjectM::RenderFrame()
     // ToDo: Call the to-be-implemented render method in Renderer
     m_activePreset->RenderFrame(audioData, renderContext);
 
-    // ToDo: Allow external apps to provide a custom target framebuffer.
     glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
+    glViewport(0, 0, renderContext.viewportSizeX, renderContext.viewportSizeY);
+
+    // On WebGL2 / Chrome ANGLE, the default framebuffer's draw buffer must
+    // be explicitly set to GL_BACK after preset rendering, which may leave
+    // per-FBO draw buffer state that leaks into FBO 0 on some drivers.
+    GLenum backBuf = GL_BACK;
+    glDrawBuffers(1, &backBuf);
 
     if (m_transition != nullptr && m_transitioningPreset != nullptr)
     {