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Compute contour indexes in a kernel and use the results to fill the grid cells

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Eryn Wells 2018-10-14 19:54:12 -07:00
parent 73bbf2196d
commit eb55566a13
3 changed files with 87 additions and 15 deletions
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28
MetaballsKit/Shaders/MarchingSquares.metal
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@ -64,6 +64,28 @@ samplingKernel(constant MarchingSquaresParameters &parameters [[buffer(0)]],
samples[idx] = sample;
}
kernel void
contouringKernel(constant MarchingSquaresParameters &parameters [[buffer(0)]],
constant float *samples [[buffer(1)]],
device ushort *contourIndexes [[buffer(2)]],
uint position [[thread_position_in_grid]])
{
// Calculate an index based on the samples at the four points around this cell.
// If the point is above the threshold, adjust the value accordingly.
// d--c 8--4
// | | -> | |
// a--b 1--2
uint a = position + parameters.gridSize.x;
uint b = position + parameters.gridSize.x + 1;
uint c = position + 1;
uint d = position;
uint index = (samples[d] >= 1.0 ? 0b1000 : 0) +
(samples[c] >= 1.0 ? 0b0100 : 0) +
(samples[b] >= 1.0 ? 0b0010 : 0) +
(samples[a] >= 1.0 ? 0b0001 : 0);
contourIndexes[position] = index;
}
vertex RasterizerData
gridVertexShader(constant Vertex *vertexes [[buffer(0)]],
constant Rect *rects [[buffer(1)]],
@ -85,9 +107,9 @@ gridVertexShader(constant Vertex *vertexes [[buffer(0)]],
fragment float4
gridFragmentShader(RasterizerData in [[stage_in]],
constant float *samples [[buffer(0)]])
constant ushort *contourIndexes [[buffer(0)]])
{
int instance = in.instance;
float sample = samples[instance];
return sample > 1.0 ? in.color : float4(0);
uint sample = contourIndexes[instance];
return sample >= 1 ? in.color : float4(0);
}