Swift - Pick Selection

Overview

Setting up Color pick id

• Creating a second render pass
• Using Blitt command to copy data
• iOS needs to be setup to copy correctly
• Is the current data transfer the best implementation

Notes:

After implementing the two texture outputs and the blit encoder, I seem to be getting a GPU Soft Fault, which is causing random frames to output garbage. It usualy is every second frame. Looking at implementing frame buffers to see if it might be a frame draw issue

2nd Draw error

There is a drawing issue when every second frame sometimes seems to be drawn as garbage. As the project does not currently use Semaphore, I think it may be a read write issue.

Reference: https://developer.apple.com/documentation/metal/synchronization/synchronizing_cpu_and_gpu_work

Fix: Was to put the texture creation outside of the draw loop

TODO

• Create a button to alternate between passes, so the viewer can see the id pass

• Instead of copying the entire image, copy just the pixel at the point of press occuring

Process

• To setup the ColourID we first need to encode the id of the object into a unique colour
• Then we need to store the colourID and object in a look up table
• Pass the colour id into the shader, so that it can be computed, and pass it to the fragment shader
• We then need to get the computed id pass back from the gpu
• Query the idPass at the point where one clicks on the screen

Resource References

• https://moddb.fandom.com/wiki/OpenGL_Selection_Using_Unique_Color_IDs
• http://www.opengl-tutorial.org/miscellaneous/clicking-on-objects/picking-with-an-opengl-hack/
• https://www.youtube.com/watch?v=OSrA1kTfwVY&t=392s