51 lines
1.9 KiB
Common Lisp
51 lines
1.9 KiB
Common Lisp
// Copyright 2017 The Servo Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// Computes total coverage and writes into the output atlas.
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//
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// This proceeds top to bottom for better data locality. For details on the algorithm, see [1].
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//
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// [1]: http://nothings.org/gamedev/rasterize/
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#define TILE_SIZE 4
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__global const int *getPixel(__global const int *gPixels, uint2 point, uint widthInTiles) {
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uint2 tile = point / TILE_SIZE, pointInTile = point % TILE_SIZE;
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return &gPixels[(tile.y * widthInTiles + tile.x) * TILE_SIZE * TILE_SIZE +
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pointInTile.y * TILE_SIZE +
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pointInTile.x];
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}
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__kernel void accum(__global const int *gPixels,
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__write_only image2d_t gTexture,
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uint4 kAtlasRect,
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uint kAtlasShelfHeight) {
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// Compute our column.
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int globalID = get_global_id(0);
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uint atlasWidth = kAtlasRect.z - kAtlasRect.x;
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uint x = globalID % atlasWidth;
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uint widthInTiles = atlasWidth / TILE_SIZE;
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// Compute the row range we'll traverse.
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uint shelf = globalID % atlasWidth;
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uint yStart = shelf * kAtlasShelfHeight;
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uint yEnd = yStart + kAtlasShelfHeight;
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// Sweep down the column, accumulating coverage as we go.
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float coverage = 0;
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for (uint y = yStart; y < yEnd; y++) {
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coverage += as_float(*getPixel(gPixels, (uint2)(x, y), widthInTiles));
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uint grayscaleValue = 255 - convert_uint(clamp(coverage, 0.0f, 255.0f));
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write_imageui(gTexture, (int2)((int)x, (int)y), (uint4)(grayscaleValue, 255, 255, 255));
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}
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}
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