39 lines
1.7 KiB
Common Lisp
39 lines
1.7 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]: https://medium.com/@raphlinus/inside-the-fastest-font-renderer-in-the-world-75ae5270c445
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const sampler_t SAMPLER = CLK_NORMALIZED_COORDS_FALSE | CLK_ADDRESS_NONE | CLK_FILTER_NEAREST;
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__kernel void accum(__write_only image2d_t gImage,
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__read_only image2d_t gCoverage,
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uint4 kAtlasRect,
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uint kAtlasShelfHeight) {
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// Determine the boundaries of the column we'll be traversing.
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uint atlasWidth = kAtlasRect.z - kAtlasRect.x;
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uint column = get_global_id(0) % atlasWidth, shelfIndex = get_global_id(0) / atlasWidth;
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uint firstRow = shelfIndex * kAtlasShelfHeight, lastRow = (shelfIndex + 1) * kAtlasShelfHeight;
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// Sweep down the column, accumulating coverage as we go.
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float coverage = 0.0f;
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for (uint row = firstRow; row < lastRow; row++) {
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int2 coord = (int2)((int)column, (int)row);
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coverage += read_imagef(gCoverage, SAMPLER, coord).r;
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float gray = fabs(coverage);
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write_imagef(gImage, coord + (int2)kAtlasRect.xy, (float4)(gray, 1.0f, 1.0f, 1.0f));
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}
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}
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