iOS-Metal: How to clear Depth Buffer ? Similar to glClear(GL_DEPTH_BUFFER_BIT) in OpenGL

Question

I need to clear the depth buffer, for which i use glClear(GL_DEPTH_BUFFER_BIT) in OpenGL, how to do in metal ? I have gone through apple's documentation, there is no hint about it.

Answer 1

The short answer is that to clear the depth buffer you add these two lines before beginning a render pass: mRenderPassDescriptor.depthAttachment.loadAction = MTLLoadActionClear; mRenderPassDescriptor.depthAttachment.clearDepth = 1.0f; And you cannot do a clear without ending and restarting a render pass.

Long answer:

In Metal, you have to define that you want the colour and depth buffers cleared when you start rendering to a MTLTexture. There is no clear function like in OpenGL.

To do this, in your MTLRenderPassDescriptor, set depthAttachment.loadAction to MTLLoadActionClear and depthAttachment.clearDepth to 1.0f. You may also want to set colorAttachments[0].loadAction to MTLLoadActionClear to clear the colour buffer.

This render pass descriptor is then passed in to your call to MTLCommandBuffer::renderCommandEncoderWithDescriptor.

If you do want to clear a depth or colour buffer midway through rendering you have to call endEncoding on MTLRenderCommandEncoder, and then start encoding again with depthAttachment.loadAction set to MTLLoadActionClear.