drawArrays without buffers

[dokipen3d]

hiya, I'm in the middle of trying out my tutorial series with MGL and have hit a couple of issues (one of which I believe is coming in a current uniform pull request by @r58Playz for mglProgramUniformMatrix4fv.

https://github.com/dokipen3d/OpenGLTutorial/tree/main/src

The other issue is that I am making a draw call that refers to its vertex locations from a const array in the shader to draw a full screen triangle. I'm hitting an assertion...

Assertion failed: (mapped_buffers == count), function -[MGLRenderer mapGLBuffersToMTLBufferMap:stage:], file MGLRenderer.m, line 511.

I haven't had time to dive deep into the library yet but is that something that should be supported?

[r58Playz]

hiya, I'm in the middle of trying out my tutorial series with MGL and have hit a couple of issues (one of which I believe is coming in a current uniform pull request by @r58Playz for mglProgramUniformMatrix4fv.

https://github.com/dokipen3d/OpenGLTutorial/tree/main/src

The other issue is that I am making a draw call that refers to its vertex locations from a const array in the shader to draw a full screen triangle. I'm hitting an assertion...

Assertion failed: (mapped_buffers == count), function -[MGLRenderer mapGLBuffersToMTLBufferMap:stage:], file MGLRenderer.m, line 511.

I haven't had time to dive deep into the library yet but is that something that should be supported?

I think in Metal you need to have some sort of vertex data to call drawarrays. You can see it in Apple's OIT example where they needed to draw a full screen quad pass. There is a seperate shader to do that and you need to draw any 6 vertices to trigger it.

edit: Here's the exact shader they have:

/// A vertex function that generates a full-screen quad pass.
/// This "dummy" vertex function is used to call blendFragments.
vertex VertexOut quadPassVertex(uint vid[[vertex_id]])
{
    VertexOut out;

    float4 position;
    position.x = (vid == 2) ? 3.0 : -1.0;
    position.y = (vid == 0) ? -3.0 : 1.0;
    position.zw = 1.0;

    out.position = position;
    return out;
}

[darkaegisagain]

In debug mode the asserts are on so if are no mapped buffers at the time primitive execution MGLRenderer will catch this. It would be best to write a bug and post a backtrace of this call under Xcode.

Mike

On Sep 1, 2022, at 7:14 AM, r58Playz @.***> wrote:

hiya, I'm in the middle of trying out my tutorial series with MGL and have hit a couple of issues (one of which I believe is coming in a current uniform pull request by @r58Playz https://github.com/r58Playz for mglProgramUniformMatrix4fv.

https://github.com/dokipen3d/OpenGLTutorial/tree/main/src https://github.com/dokipen3d/OpenGLTutorial/tree/main/src The other issue is that I am making a draw call that refers to its vertex locations from a const array in the shader to draw a full screen triangle. I'm hitting an assertion...

Assertion failed: (mapped_buffers == count), function -[MGLRenderer mapGLBuffersToMTLBufferMap:stage:], file MGLRenderer.m, line 511.

I haven't had time to dive deep into the library yet but is that something that should be supported?

I think in Metal you need to have some sort of vertex data to call drawarrays. You can see it in Apple's OIT example https://developer.apple.com/documentation/metal/metal_sample_code_library/implementing_order-independent_transparency_with_image_blocks?changes=_5__4 where they needed to draw a full screen quad pass. There is a seperate shader to do that and you need to draw any 6 vertices to trigger it.

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