The screen is blank white when my app is started, but will go to normal once the screen is touched.
The error below comes up:
ERROR /BuildRoot/Library/Caches/com.apple.xbs/Sources/VectorKit_Sim/VectorKit-1230.34.9.30.27/GeoGL/GeoGL/GLCoreContext.cpp 1763: InfoLog SolidRibbonShader:
ERROR /BuildRoot/Library/Caches/com.apple.xbs/Sources/VectorKit_Sim/VectorKit-1230.34.9.30.27/GeoGL/GeoGL/GLCoreContext.cpp 1764: WARNING: Output of vertex shader 'v_gradient' not read by fragment shader
How can I fix this?
Vertex Shaders generally run directly on the GPU for which it's compiled. In this case the iOS simulator doesn't physically have the GPU it needs to work with, hence the white screen.
Usually if you run the code on the physical device it should work, so try running there. Also check out this other question/answer with a similar error that might be of interest.
A vertex shader is simply a tiny program that runs on the GPU, written in a C++ like language called the Metal Shading Language.