How to Use Multiple Mtlrenderpipelinestates in One Mtlrendercommandencoder

Can I use multiple MTLRenderPipelineStates in one MTLRenderCommandEncoder?

Yes, you can use multiple pipeline states in one render command encoder. That's precisely why the setRenderPipelineState() method exists, rather than the pipeline state being part of the render pass descriptor. The properties in the render pass descriptor are only read at the time of the creation of the render command encoder and can't be changed during the lifetime of that encoder. Anything which is independently settable on the encoder can be changed during its lifetime.

Using multiple render pipelines in a single MTLRenderCommandEncoder: How to Synchronize MTLBuffer?

I believe you need to use separate encoders. In this (somewhat dated) documentation about function writes, only atomic operations are synchronized for buffers shared between draw calls.

How to combine Render Command Encoders that use a different shader in Metal

But, if I understood well Metal documentation, you need to define all your passes "statically", that is, you need a different Render Command Encoder for every shader and render surfaces configurations that you use. Is this correct?

No, that's not entirely correct. You'll notice that there are some attributes of a render command encoder that are specified via the MTLRenderPassDescriptor at the time you create the encoder, and there are other attributes that are set via accessors on the encoder after it has been created. The former are immutable for the lifetime of the encoder. The latter can be changed.

So, you do need a new command encoder if you change the render targets (attachments). But you do not need a new command encoder to change the shaders. The shaders are specified by the render pipeline state and can be changed on an existing command encoder using setRenderPipelineState(_:).

It is definitely true that you should create your render pipeline state objects once in the lifetime of the app, if at all possible. But you can reuse them as often as needed after that.

Finally, I would not worry too much about creating multiple render command encoders. They are designed to be relatively cheap to create. So, while expending a bit of effort to consolidate all work which can be done with a given encoder together is fine, don't bend over backwards to try to make something "simpler" when it runs against the grain of how things work.

Metal: limit MTLRenderCommandEncoder texture loading to only part of texture

One approach, to avoid loading and storing the entire texture into the render pipeline, could be the following, assuming your scissor rectangle is constant between drawcalls:

1. Blit (MTLBlitCommandEncoder) the region of interest from the large texture to a smaller(e.g. the size of your scissor rectangle) intermediate texture.

2. Load and store, and draw/operate only on the smaller intermediate texture.

3. When done encoding, blit back the result to the original source region of the larger texture.

This way you load and store only the region of interest in your pipeline, with only the added constant memory cost of maintaining a smaller intermediate texture(assuming region of interest is constant between drawcalls).

Blitting is a fast operation and the above method should thus optimize your current pipeline.

How to use different fragment shaders in one Metal API scene?

You can use multiple fragment shaders in a single frame/pass by creating multiple render pipeline states. Simply create a pipeline state for each vertex/fragment function pair, and call setRenderPipelineState: on your render command encoder to set the appropriate pipeline state before issuing the draw call. You will need to write separate fragment shader functions for doing the color passthrough and the texture sampling.

Metal blending alpha under 0.5

Solved. The problem was that alphaToCoverageEnabled was set to true, while the render target texture type was NOT MTLTextureType2DMultisample. It appears the two work in tandem, but it's beyond my understanding how.

If not using multi-sampling, set alphaToCoverageEnabled to false.

Otherwise, make sure the render target is of type MTLTextureType2DMultisample.

If using MTKView, set the render target texture type by setting the sampleCount on the MTKView object:

    _view = (MTKView *)self.view;
    _view.sampleCount = 2;

and the render pipeline descriptor of the pipeline state:

    MTLRenderPipelineDescriptor *pd = [[MTLRenderPipelineDescriptor alloc] init];
    pd.sampleCount = 2;

iOS Metal - rendering a complete triangle

I can see a small mistake in the setting of vertices that could be causing this.

func floatBuffer() -> [Float]{
        return [x,y,x,r,g,b,a]
    }

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