The latest in the series, OpenGL ES 3.2 added additional functionality based on the Android Extension Pack for OpenGL ES 3.1, which brought the mobile API's functionality significantly closer to it's desktop counterpart - OpenGL. You need to do that so that you don't get R, G or B components greater than the alpha value, which is illegal when using premultiplied alpha and was probably the cause of transparent colours not being drawn.OpenGL ES API Versions at a Glance OpenGL ES 3.2 - Additional OpenGL functionality When adjusting colours in the fragment shader, multiply all components of the colour by the alpha value: gl_FragColor *= vec4(alpha) instead of gl_FragColor.w *= alpha. Use premultiplied alpha for all transparent colours. Use the blend function glBlendFunc(GL_ONE,GL_ONE_MINUS_SRC_ALPHA). This can be done in the standard way by adding #define statements to define lowp, mediump and highp as nothing, at the start of the shader program, and doing that only on the affected platform (Qt on the Mac). Remove all the precision qualifiers or statements from the shader programs. The reason for the problem seems to be twofold: the shader compiler doesn't support the OpenGL ES version of the GLSL shader language, and the OpenGL ES implementation doesn't support all the blending modes, in particular glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA). It works, but I'm still interested in better fixes and explanations of what exactly is going on. Is there a solution to this problem? I have spent a few hours searching and found nothing. I am confident of the correctness of my use of OpenGL ES 2.0, because, apart from working under Qt on Windows and Linux, the same code also works perfectly outside Qt on Android (in native code) and iOS.Īccording the the Qt documentation, QOpenGLFunctions 'provides cross-platform access to the OpenGL ES 2.0 API'. I discovered that only pixels with no transparency (alpha = 1) were drawn. However, the display was incorrect - some graphics were missing. I found I could get some graphics on the display by deleting the 'precision' statements from the shaders. I tried inserting '#version 100' at the start of the shader programs, but that didn't help: the error message this time was that version 100 was not supported. This probably indicates that the shader compiler expects a different version of the shader language. When I first tried running the app it crashed because it could not compile the shader programs, complaining that the 'precision' keyword was syntactically incorrect. However, on the Mac, drawing the graphics does not work.

I use Qt 5 and Qt Creator on all three platforms. Everything works perfectly (using the same Qt app) on Windows and Linux. It draws using OpenGL ES 2.0, using QOpenGLFunctions to resolve the OpenGL functions. I have a Qt app that uses a QOpenGLWidget for its main window.

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