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static const char *hb_gpu_paint_fragment_wgsl =
"/*\n"
" * Copyright (C) 2026 Behdad Esfahbod\n"
" *\n"
" * This is part of HarfBuzz, a text shaping library.\n"
" *\n"
" * Permission is hereby granted, without written agreement and without\n"
" * license or royalty fees, to use, copy, modify, and distribute this\n"
" * software and its documentation for any purpose, provided that the\n"
" * above copyright notice and the following two paragraphs appear in\n"
" * all copies of this software.\n"
" *\n"
" * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR\n"
" * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES\n"
" * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN\n"
" * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH\n"
" * DAMAGE.\n"
" *\n"
" * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,\n"
" * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND\n"
" * FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS\n"
" * ON AN \"AS IS\" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO\n"
" * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.\n"
" */\n"
"\n"
"\n"
"/* Paint-renderer fragment shader (WGSL).\n"
" *\n"
" * Assumes the shared fragment helpers (hb-gpu-fragment.wgsl) and\n"
" * the draw-renderer fragment helpers (hb-gpu-draw-fragment.wgsl)\n"
" * are prepended to this source.\n"
" *\n"
" * atlas is passed as an explicit storage-buffer pointer parameter,\n"
" * matching WGSL's scoping rules.\n"
" */\n"
"\n"
"\n"
"fn _hb_gpu_stop_color (hb_gpu_atlas: ptr<storage, array<vec4<i32>>, read>,\n"
" stops_base: i32, i: i32, foreground: vec4f,\n"
" offset: ptr<function, f32>) -> vec4f\n"
"{\n"
" let a = hb_gpu_fetch (hb_gpu_atlas, stops_base + i * 2);\n"
" *offset = f32 (a.r) / 32767.0;\n"
" let b = hb_gpu_fetch (hb_gpu_atlas, stops_base + i * 2 + 1);\n"
" if ((a.g & 1) != 0) {\n"
" return vec4f (foreground.rgb, foreground.a * (f32 (b.a) / 32767.0));\n"
" }\n"
" return vec4f (b) / 32767.0;\n"
"}\n"
"\n"
"fn _hb_gpu_extend_t (t: f32, extend: i32) -> f32\n"
"{\n"
" if (extend == 1) { return t - floor (t); }\n"
" if (extend == 2) {\n"
" let u = t - 2.0 * floor (t * 0.5);\n"
" if (u > 1.0) { return 2.0 - u; }\n"
" return u;\n"
" }\n"
" return clamp (t, 0.0, 1.0);\n"
"}\n"
"\n"
"fn _hb_gpu_eval_stops (hb_gpu_atlas: ptr<storage, array<vec4<i32>>, read>,\n"
" stops_base: i32, stop_count: i32,\n"
" t: f32, foreground: vec4f) -> vec4f\n"
"{\n"
" var off_prev: f32;\n"
" var col_prev = _hb_gpu_stop_color (hb_gpu_atlas, stops_base, 0, foreground, &off_prev);\n"
" if (t <= off_prev) { return col_prev; }\n"
" for (var i: i32 = 1; i < stop_count; i = i + 1)\n"
" {\n"
" var off: f32;\n"
" let col = _hb_gpu_stop_color (hb_gpu_atlas, stops_base, i, foreground, &off);\n"
" if (t <= off)\n"
" {\n"
" let span = off - off_prev;\n"
" var f: f32 = 0.0;\n"
" if (span > 1e-6) { f = (t - off_prev) / span; }\n"
" let p0 = vec4f (col_prev.rgb * col_prev.a, col_prev.a);\n"
" let p1 = vec4f (col.rgb * col.a, col.a);\n"
" let pm = mix (p0, p1, f);\n"
" if (pm.a > 1e-6) { return vec4f (pm.rgb / pm.a, pm.a); }\n"
" return vec4f (0.0);\n"
" }\n"
" col_prev = col;\n"
" off_prev = off;\n"
" }\n"
" return col_prev;\n"
"}\n"
"\n"
"/* Apply the stored 2x2 M^-1 (row-major i16 Q10) to a vector. */\n"
"fn _hb_gpu_apply_minv (m: vec4<i32>, v: vec2f) -> vec2f\n"
"{\n"
" let mf = vec4f (m) * (1.0 / 1024.0);\n"
" return vec2f (mf.x * v.x + mf.y * v.y,\n"
" mf.z * v.x + mf.w * v.y);\n"
"}\n"
"\n"
"fn _hb_gpu_sample_linear (renderCoord: vec2f, grad_base: i32,\n"
" stop_count: i32, extend: i32, foreground: vec4f,\n"
" hb_gpu_atlas: ptr<storage, array<vec4<i32>>, read>) -> vec4f\n"
"{\n"
" let t0 = hb_gpu_fetch (hb_gpu_atlas, grad_base);\n"
" let m = hb_gpu_fetch (hb_gpu_atlas, grad_base + 1);\n"
" let p0_r = vec2f (f32 (t0.r), f32 (t0.g));\n"
" let d = vec2f (f32 (t0.b), f32 (t0.a));\n"
" let denom = dot (d, d);\n"
" if (denom < 1e-6) { return vec4f (0.0); }\n"
" let p = _hb_gpu_apply_minv (m, renderCoord - p0_r);\n"
" var t = dot (p, d) / denom;\n"
" t = _hb_gpu_extend_t (t, extend);\n"
" return _hb_gpu_eval_stops (hb_gpu_atlas, grad_base + 2, stop_count, t, foreground);\n"
"}\n"
"\n"
"fn _hb_gpu_sample_radial (renderCoord: vec2f, grad_base: i32,\n"
" stop_count: i32, extend: i32, foreground: vec4f,\n"
" hb_gpu_atlas: ptr<storage, array<vec4<i32>>, read>) -> vec4f\n"
"{\n"
" let t0 = hb_gpu_fetch (hb_gpu_atlas, grad_base);\n"
" let t1 = hb_gpu_fetch (hb_gpu_atlas, grad_base + 1);\n"
" let m = hb_gpu_fetch (hb_gpu_atlas, grad_base + 2);\n"
" let c0_r = vec2f (f32 (t0.r), f32 (t0.g));\n"
" let cd = vec2f (f32 (t0.b), f32 (t0.a));\n"
" let r0 = f32 (t1.r);\n"
" let r1 = f32 (t1.g);\n"
"\n"
" let dr = r1 - r0;\n"
" let p = _hb_gpu_apply_minv (m, renderCoord - c0_r);\n"
"\n"
" let A = dot (cd, cd) - dr * dr;\n"
" let B = -2.0 * (dot (p, cd) + r0 * dr);\n"
" let C = dot (p, p) - r0 * r0;\n"
"\n"
" var t: f32;\n"
" if (abs (A) > 1e-6)\n"
" {\n"
" let disc = B * B - 4.0 * A * C;\n"
" if (disc < 0.0) { return vec4f (0.0); }\n"
" let sq = sqrt (disc);\n"
" let t1r = (-B + sq) / (2.0 * A);\n"
" let t2r = (-B - sq) / (2.0 * A);\n"
" if (r0 + t1r * dr >= 0.0) { t = t1r; } else { t = t2r; }\n"
" }\n"
" else\n"
" {\n"
" if (abs (B) < 1e-6) { return vec4f (0.0); }\n"
" t = -C / B;\n"
" }\n"
" t = _hb_gpu_extend_t (t, extend);\n"
" return _hb_gpu_eval_stops (hb_gpu_atlas, grad_base + 3, stop_count, t, foreground);\n"
"}\n"
"\n"
"fn _hb_gpu_sample_sweep (renderCoord: vec2f, grad_base: i32,\n"
" stop_count: i32, extend: i32, foreground: vec4f,\n"
" hb_gpu_atlas: ptr<storage, array<vec4<i32>>, read>) -> vec4f\n"
"{\n"
" let t0 = hb_gpu_fetch (hb_gpu_atlas, grad_base);\n"
" let m = hb_gpu_fetch (hb_gpu_atlas, grad_base + 1);\n"
" let c_r = vec2f (f32 (t0.r), f32 (t0.g));\n"
" let a0 = f32 (t0.b) / 16384.0;\n"
" let a1 = f32 (t0.a) / 16384.0;\n"
" let span = a1 - a0;\n"
" if (abs (span) < 1e-6) { return vec4f (0.0); }\n"
"\n"
" let p = _hb_gpu_apply_minv (m, renderCoord - c_r);\n"
" var ang = atan2 (p.y, p.x) / 3.14159265358979;\n"
" if (ang < 0.0) { ang = ang + 2.0; }\n"
" var t = (ang - a0) / span;\n"
" t = _hb_gpu_extend_t (t, extend);\n"
" return _hb_gpu_eval_stops (hb_gpu_atlas, grad_base + 2, stop_count, t, foreground);\n"
"}\n"
"\n"
"fn _hb_gpu_composite (src: vec4f, dst: vec4f, mode_in: i32) -> vec4f\n"
"{\n"
" var r = src + dst * (1.0 - src.a); /* SRC_OVER default */\n"
"\n"
" /* Mode numbers match hb_paint_composite_mode_t. Approximate\n"
" * unsupported modes with the nearest Porter-Duff mode we do\n"
" * implement; DIFFERENCE / EXCLUSION / HSL_* still fall through to\n"
" * SRC_OVER below. */\n"
" var mode = mode_in;\n"
" if (mode == 14 || mode == 18 || mode == 19) { mode = 23; } /* OVERLAY / COLOR_BURN / HARD_LIGHT -> MULTIPLY */\n"
" else if (mode == 17 || mode == 20) { mode = 13; } /* COLOR_DODGE / SOFT_LIGHT -> SCREEN */\n"
"\n"
" if (mode == 0) { r = vec4f (0.0); } /* CLEAR */\n"
" else if (mode == 1) { r = src; } /* SRC */\n"
" else if (mode == 2) { r = dst; } /* DST */\n"
" else if (mode == 4) { r = dst + src * (1.0 - dst.a); } /* DST_OVER */\n"
" else if (mode == 5) { r = src * dst.a; } /* SRC_IN */\n"
" else if (mode == 6) { r = dst * src.a; } /* DST_IN */\n"
" else if (mode == 7) { r = src * (1.0 - dst.a); } /* SRC_OUT */\n"
" else if (mode == 8) { r = dst * (1.0 - src.a); } /* DST_OUT */\n"
" else if (mode == 9) { r = src * dst.a + dst * (1.0 - src.a); } /* SRC_ATOP */\n"
" else if (mode == 10) { r = dst * src.a + src * (1.0 - dst.a); } /* DST_ATOP */\n"
" else if (mode == 11) { r = src * (1.0 - dst.a) + dst * (1.0 - src.a); } /* XOR */\n"
" else if (mode == 12) { r = min (src + dst, vec4f (1.0)); } /* PLUS */\n"
" else if (mode == 13) { /* SCREEN (premul) */\n"
" r = vec4f (src.rgb + dst.rgb - src.rgb * dst.rgb,\n"
" src.a + dst.a - src.a * dst.a);\n"
" }\n"
" else if (mode == 15) { /* DARKEN */\n"
" r = vec4f (min (src.rgb * dst.a, dst.rgb * src.a)\n"
" + src.rgb * (1.0 - dst.a) + dst.rgb * (1.0 - src.a),\n"
" src.a + dst.a - src.a * dst.a);\n"
" }\n"
" else if (mode == 16) { /* LIGHTEN */\n"
" r = vec4f (max (src.rgb * dst.a, dst.rgb * src.a)\n"
" + src.rgb * (1.0 - dst.a) + dst.rgb * (1.0 - src.a),\n"
" src.a + dst.a - src.a * dst.a);\n"
" }\n"
" else if (mode == 23) { /* MULTIPLY (premul) */\n"
" r = vec4f (src.rgb * (1.0 - dst.a) + dst.rgb * (1.0 - src.a)\n"
" + src.rgb * dst.rgb,\n"
" src.a + dst.a - src.a * dst.a);\n"
" }\n"
" /* SRC_OVER (3) and DIFFERENCE / EXCLUSION / HSL_* (21, 22, 24-27)\n"
" * fall through to the SRC_OVER default. */\n"
" return r;\n"
"}\n"
"\n"
"/* Wrap _hb_gpu_slug with a sub-glyph extents bail-out. Many\n"
" * paint layers cover a small region of the outer glyph quad; for\n"
" * fragments outside the layer's bbox (with an AA + MSAA-spread\n"
" * margin) the slug coverage is exactly 0, so we can skip the\n"
" * band/curve walk entirely. */\n"
"fn _hb_gpu_slug_clipped (renderCoord: vec2f, pixelsPerEm: vec2f, glyphLoc_: u32,\n"
" hb_gpu_atlas: ptr<storage, array<vec4<i32>>, read>) -> f32\n"
"{\n"
" let header0 = hb_gpu_fetch (hb_gpu_atlas, i32 (glyphLoc_));\n"
" let ext = vec4f (header0) * HB_GPU_INV_UNITS;\n"
" let margin = 2.0 / pixelsPerEm;\n"
" if (any (renderCoord < ext.xy - margin) ||\n"
" any (renderCoord > ext.zw + margin)) {\n"
" return 0.0;\n"
" }\n"
" return _hb_gpu_slug (renderCoord, pixelsPerEm, glyphLoc_, hb_gpu_atlas);\n"
"}\n"
"\n"
"/* Combine slug coverages from all clip outlines on the layer.\n"
" * Factored so the shader has one set of inlined slug walks\n"
" * instead of two (one per LAYER op type). flags bits: 0x100 =\n"
" * HAS_CLIP2; 0x200 = HAS_CLIP3 (HAS_CLIP3 implies HAS_CLIP2). */\n"
"fn _hb_gpu_layer_coverage (renderCoord: vec2f, pixelsPerEm: vec2f,\n"
" base: i32, flags: i32,\n"
" clip1_payload: i32, clip2_payload: i32, clip3_payload: i32,\n"
" hb_gpu_atlas: ptr<storage, array<vec4<i32>>, read>) -> f32\n"
"{\n"
" var cov = _hb_gpu_slug_clipped (renderCoord, pixelsPerEm,\n"
" u32 (base + clip1_payload), hb_gpu_atlas);\n"
" if ((flags & 0x100) != 0) {\n"
" cov = cov * _hb_gpu_slug_clipped (renderCoord, pixelsPerEm,\n"
" u32 (base + clip2_payload), hb_gpu_atlas);\n"
" if ((flags & 0x200) != 0) {\n"
" cov = cov * _hb_gpu_slug_clipped (renderCoord, pixelsPerEm,\n"
" u32 (base + clip3_payload), hb_gpu_atlas);\n"
" }\n"
" }\n"
" return cov;\n"
"}\n"
"\n"
"const HB_GPU_PAINT_GROUP_DEPTH: i32 = 4;\n"
"\n"
"fn hb_gpu_paint (renderCoord: vec2f, glyphLoc_: u32, foreground: vec4f,\n"
" hb_gpu_atlas: ptr<storage, array<vec4<i32>>, read>,\n"
" coverage: ptr<function, f32>) -> vec4f\n"
"{\n"
" /* Compute pixelsPerEm once here at uniform control flow. WGSL\n"
" * rejects fwidth inside a loop-conditional branch, so we call\n"
" * _hb_gpu_slug (the MSAA-aware implementation that takes a\n"
" * pre-computed pixelsPerEm) instead of the top-level\n"
" * hb_gpu_draw() which would re-call fwidth. */\n"
" let emsPerPixel = fwidth (renderCoord);\n"
" let pixelsPerEm = 1.0 / emsPerPixel;\n"
"\n"
" let base = i32 (glyphLoc_);\n"
" let h0 = hb_gpu_fetch (hb_gpu_atlas, base); // (num_ops, _, _, _)\n"
" let h2 = hb_gpu_fetch (hb_gpu_atlas, base + 2); // (ops_offset, _, _, _)\n"
" let num_ops = h0.r;\n"
" var cursor = base + h2.r;\n"
"\n"
" var acc = vec4f (0.0);\n"
" var group_stack: array<vec4f, HB_GPU_PAINT_GROUP_DEPTH>;\n"
" var sp: i32 = 0;\n"
" *coverage = 0.0;\n"
"\n"
" for (var i: i32 = 0; i < num_ops; i = i + 1)\n"
" {\n"
" let op = hb_gpu_fetch (hb_gpu_atlas, cursor);\n"
" let op_type = op.r;\n"
" let aux = op.g;\n"
" let payload = (op.b << 16) | (op.a & 0xffff);\n"
"\n"
" if (op_type == 0) { // LAYER_SOLID\n"
" // texel 1: (clip2_hi, clip2_lo, clip3_hi, clip3_lo) -- valid\n"
" // per HAS_CLIP2 / HAS_CLIP3 flag bits.\n"
" // texel 2: RGBA as signed Q15.\n"
" let op2 = hb_gpu_fetch (hb_gpu_atlas, cursor + 1);\n"
" let clip2_payload = (op2.r << 16) | (op2.g & 0xffff);\n"
" let clip3_payload = (op2.b << 16) | (op2.a & 0xffff);\n"
" let ct = hb_gpu_fetch (hb_gpu_atlas, cursor + 2);\n"
" var col: vec4f;\n"
" if ((aux & 1) != 0) {\n"
" col = vec4f (foreground.rgb, foreground.a * (f32 (ct.a) / 32767.0));\n"
" } else {\n"
" col = vec4f (ct) / 32767.0;\n"
" }\n"
"\n"
" let cov = _hb_gpu_layer_coverage (renderCoord, pixelsPerEm,\n"
" base, aux,\n"
" payload, clip2_payload, clip3_payload,\n"
" hb_gpu_atlas);\n"
" *coverage = max (*coverage, cov);\n"
" let src = vec4f (col.rgb * col.a, col.a) * cov;\n"
" acc = src + acc * (1.0 - src.a);\n"
"\n"
" cursor = cursor + 3;\n"
" } else if (op_type == 1) { // LAYER_GRADIENT\n"
" let op2 = hb_gpu_fetch (hb_gpu_atlas, cursor + 1);\n"
" let clip2_payload = (op2.r << 16) | (op2.g & 0xffff);\n"
" let clip3_payload = (op2.b << 16) | (op2.a & 0xffff);\n"
" let op3 = hb_gpu_fetch (hb_gpu_atlas, cursor + 2);\n"
" let grad_payload = (op3.r << 16) | (op3.g & 0xffff);\n"
" let extend = op3.b;\n"
" let stop_count = op3.a;\n"
" let subtype = aux & 0xff;\n"
"\n"
" var col = vec4f (0.0);\n"
" if (subtype == 0) {\n"
" col = _hb_gpu_sample_linear (renderCoord,\n"
" base + grad_payload,\n"
" stop_count, extend, foreground,\n"
" hb_gpu_atlas);\n"
" } else if (subtype == 1) {\n"
" col = _hb_gpu_sample_radial (renderCoord,\n"
" base + grad_payload,\n"
" stop_count, extend, foreground,\n"
" hb_gpu_atlas);\n"
" } else if (subtype == 2) {\n"
" col = _hb_gpu_sample_sweep (renderCoord,\n"
" base + grad_payload,\n"
" stop_count, extend, foreground,\n"
" hb_gpu_atlas);\n"
" }\n"
"\n"
" let cov = _hb_gpu_layer_coverage (renderCoord, pixelsPerEm,\n"
" base, aux,\n"
" payload, clip2_payload, clip3_payload,\n"
" hb_gpu_atlas);\n"
" *coverage = max (*coverage, cov);\n"
" let src = vec4f (col.rgb * col.a, col.a) * cov;\n"
" acc = src + acc * (1.0 - src.a);\n"
"\n"
" cursor = cursor + 3;\n"
" } else if (op_type == 2) { // PUSH_GROUP\n"
" if (sp < HB_GPU_PAINT_GROUP_DEPTH) {\n"
" group_stack[sp] = acc;\n"
" sp = sp + 1;\n"
" }\n"
" acc = vec4f (0.0);\n"
" cursor = cursor + 1;\n"
" } else if (op_type == 3) { // POP_GROUP\n"
" if (sp > 0) {\n"
" sp = sp - 1;\n"
" let src = acc;\n"
" let dst = group_stack[sp];\n"
" acc = _hb_gpu_composite (src, dst, aux);\n"
" }\n"
" cursor = cursor + 1;\n"
" } else {\n"
" break;\n"
" }\n"
" }\n"
"\n"
" return acc;\n"
"}\n"
;