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notes

In metal nvg there are two types of functions. First type start with the name "render" and are set is the one set as a function pointer on the nvgcontext.

params.renderCreate = mtlnvg__renderCreate;
params.renderCreateTexture = mtlnvg__renderCreateTexture;
params.renderDeleteTexture = mtlnvg__renderDeleteTexture;
params.renderUpdateTexture = mtlnvg__renderUpdateTexture;
params.renderGetTextureSize = mtlnvg__renderGetTextureSize;
params.renderViewport = mtlnvg__renderViewport;
params.renderCancel = mtlnvg__renderCancel;
params.renderFlush = mtlnvg__renderFlush;
params.renderFill = mtlnvg__renderFill;
params.renderStroke = mtlnvg__renderStroke;
params.renderTriangles = mtlnvg__renderTriangles;
params.renderDelete = mtlnvg__renderDelete;
params.userPtr = (__bridge_retained void*)mtl;
params.edgeAntiAlias = flags & NVG_ANTIALIAS ? 1 : 0;

The second type are called fill, convexFill, stroke & triangles. These are used in the renderFlush function. They set the state on the encoder. Each function takes a MNVGcall argument.

I guess gpucanvas only requires you do implement the second type.

if (call->type == MNVG_FILL)
    [self fill:call];
else if (call->type == MNVG_CONVEXFILL)
    [self convexFill:call];
else if (call->type == MNVG_STROKE)
    [self stroke:call];
else if (call->type == MNVG_TRIANGLES)
    [self triangles:call];
// Create indices for a triangle fan. (This is OK because the clipped quad should always be
// convex.)
let mut indices: Vec<u32> = vec![];
for index in 1..(quad_positions.len() as u32 - 1) {
    indices.extend_from_slice(&[0, index as u32, index + 1]);
}

triangle fan

  • based on pathfinder
// https://www.gamedev.net/forums/topic/643945-how-to-generate-a-triangle-fan-index-list-for-a-circle-shape/

fn triangle_fan_indices(len: usize) -> Vec<u32> {
	let mut indices: Vec<u32> = vec![];
	for index in 1..(len as u32 - 1) {
		indices.extend_from_slice(&[0, index as u32, index + 1]);
	}

	indices
}

fn main() {
	let indices = triangle_fan_indices(10);
	println!("{:?}", indices);
}

TODO

  • investigate setViewport vs uniforms
  • indexed rendering
  • what is composite operation?
  • vert_arr vs vert_buf

convex_fill

| gpucanvas | metal | | render | renderflush | | renderGetTextureSizeForImage

  • concave_fill

    • this is called fill in metalnvg

    • fundamentally, there are these steps

      • set stencil
      • uniforms (missing in mnvg)
      • draw shapes *
      • restore states
      • draw anti-aliased fragments
      • draw fill
  • stroking
    • gpucanvas, unlike metalnvg, separates stroke and stencil_stroke into two functions
    • stencil stroke
      • fill the stroke and base without overlap
        • set uniform
        • setdepthstencilstate
        • setrenderpipelinestate
        • draw trianglestrip
      • drawn antialiased fragments
        • setuniform
        • setdepthstencilstate
        • draw trianglestrip
      • clear stencil buffer
        • setdepthstencilstate
        • setrenderpipelinestate
        • draw trianglestrip
        • setdepthstencilstate default