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.
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;
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
.
To explain the solution more clear with sample codes
Before start rendering:
void prepareRendering(){
CMDBuffer = [_commandQueue commandBuffer]; // get command Buffer
drawable = [_metalLayer nextDrawable]; // get drawable from metalLayer
renderingTexture = drawable.texture; // set that as rendering te
setupRenderPassDescriptorForTexture(drawable.texture); // set the depth and colour buffer properties
RenderCMDBuffer = [CMDBuffer renderCommandEncoderWithDescriptor:_renderPassDescriptor];
RenderCMDBuffer.label = @"MyRenderEncoder";
setUpDepthState(CompareFunctionLessEqual,true,false); //
[RenderCMDBuffer setDepthStencilState:_depthState];
[RenderCMDBuffer pushDebugGroup:@"DrawCube"];
}
void setupRenderPassDescriptorForTexture(id <MTLTexture> texture)
{
if (_renderPassDescriptor == nil)
_renderPassDescriptor = [MTLRenderPassDescriptor renderPassDescriptor];
// set color buffer properties
_renderPassDescriptor.colorAttachments[0].texture = texture;
_renderPassDescriptor.colorAttachments[0].loadAction = MTLLoadActionClear;
_renderPassDescriptor.colorAttachments[0].clearColor = MTLClearColorMake(1.0f, 1.0f,1.0f, 1.0f);
_renderPassDescriptor.colorAttachments[0].storeAction = MTLStoreActionStore;
// set depth buffer properties
MTLTextureDescriptor* desc = [MTLTextureDescriptor texture2DDescriptorWithPixelFormat: MTLPixelFormatDepth32Float width: texture.width height: texture.height mipmapped: NO];
_depthTex = [device newTextureWithDescriptor: desc];
_depthTex.label = @"Depth";
_renderPassDescriptor.depthAttachment.texture = _depthTex;
_renderPassDescriptor.depthAttachment.loadAction = MTLLoadActionClear;
_renderPassDescriptor.depthAttachment.clearDepth = 1.0f;
_renderPassDescriptor.depthAttachment.storeAction = MTLStoreActionDontCare;
}
Render Your contents here
Render();
After rendering
similar to ogles2 method [_context presentRenderbuffer:_colorRenderBuffer];
void endDisplay()
{
[RenderCMDBuffer popDebugGroup];
[RenderCMDBuffer endEncoding];
[CMDBuffer presentDrawable:drawable];
[CMDBuffer commit];
_currentDrawable = nil;
}
The above methods clears the depth and colour buffers after rendering each frame
To clear the depth buffer in midway
void clearDepthBuffer(){
// end encoding the render command buffer
[RenderCMDBuffer popDebugGroup];
[RenderCMDBuffer endEncoding];
// here MTLLoadActionClear will clear your last drawn depth values
_renderPassDescriptor.depthAttachment.loadAction = MTLLoadActionClear; _renderPassDescriptor.depthAttachment.clearDepth = 1.0f;
_renderPassDescriptor.depthAttachment.storeAction = MTLStoreActionDontCare;
// here MTLLoadActionLoad will reuse your last drawn color buffer
_renderPassDescriptor.colorAttachments[0].loadAction = MTLLoadActionLoad;
_renderPassDescriptor.colorAttachments[0].storeAction = MTLStoreActionStore;
RenderCMDBuffer = [CMDBuffer renderCommandEncoderWithDescriptor:_renderPassDescriptor];
RenderCMDBuffer.label = @"MyRenderEncoder";
[RenderCMDBuffer pushDebugGroup:@"DrawCube"];
}
Here is the Swift 5 version. Run your first render pass:
// RENDER PASS 1
renderPassDescriptor = view.currentRenderPassDescriptor
if let renderPassDescriptor = renderPassDescriptor, let renderEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: renderPassDescriptor) {
renderEncoder.label = "First Render Encoder"
renderEncoder.pushDebugGroup("First Render Debug")
// render stuff here...
renderEncoder.popDebugGroup()
renderEncoder.endEncoding()
}
Then clear the depth buffer, but keep the colour buffer:
renderPassDescriptor = view.currentRenderPassDescriptor
// Schedule Metal to clear the depth buffer
renderPassDescriptor!.depthAttachment.loadAction = MTLLoadAction.clear
renderPassDescriptor!.depthAttachment.clearDepth = 1.0
renderPassDescriptor!.depthAttachment.storeAction = MTLStoreAction.dontCare
// Schedule Metal to reuse the previous colour buffer
renderPassDescriptor!.colorAttachments[0].loadAction = MTLLoadAction.load
renderPassDescriptor!.colorAttachments[0].storeAction = MTLStoreAction.store
Then run your second render:
if let renderPassDescriptor = renderPassDescriptor, let renderEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: renderPassDescriptor) {
renderEncoder.label = "Second Render"
renderEncoder.pushDebugGroup("Second Render Debug")
// render stuff here...
renderEncoder.popDebugGroup()
renderEncoder.endEncoding()
}
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