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Continue wiring up gpu-side flattening

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All segments given to path coarse raster are cubics. Flatten to
quadratics.

This works but the quality is not (yet) good.
This commit is contained in:
Raph Levien 2020-06-09 17:20:58 -07:00
parent 0f44bc8b78
commit b571e0d10c
5 changed files with 118 additions and 69 deletions
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27
piet-gpu/shader/elements.comp
View file

@ -318,29 +318,34 @@ void main() {
case Element_StrokeLine:
LineSeg line = Element_StrokeLine_read(this_ref);
PathStrokeLine path_line;
path_line.p0 = st.mat.xy * line.p0.x + st.mat.zw * line.p0.y + st.translate;
path_line.p1 = st.mat.xy * line.p1.x + st.mat.zw * line.p1.y + st.translate;
path_line.path_ix = st.path_count;
vec2 p0 = st.mat.xy * line.p0.x + st.mat.zw * line.p0.y + st.translate;
vec2 p1 = st.mat.xy * line.p1.x + st.mat.zw * line.p1.y + st.translate;
PathStrokeCubic path_cubic;
path_cubic.p0 = p0;
path_cubic.p1 = mix(p0, p1, 1.0 / 3.0);
path_cubic.p2 = mix(p1, p0, 1.0 / 3.0);
path_cubic.p3 = p1;
path_cubic.path_ix = st.path_count;
if (tag == Element_StrokeLine) {
path_line.stroke = get_linewidth(st);
path_cubic.stroke = get_linewidth(st);
} else {
path_line.stroke = vec2(0.0);
path_cubic.stroke = vec2(0.0);
}
// We do encoding a bit by hand to minimize divergence. Another approach
// would be to have a fill/stroke bool.
PathSegRef path_out_ref = PathSegRef((st.pathseg_count - 1) * PathSeg_size);
uint out_tag = tag == Element_FillLine ? PathSeg_FillLine : PathSeg_StrokeLine;
uint out_tag = tag == Element_FillLine ? PathSeg_FillCubic : PathSeg_StrokeCubic;
pathseg[path_out_ref.offset >> 2] = out_tag;
PathStrokeLine_write(PathStrokeLineRef(path_out_ref.offset + 4), path_line);
PathStrokeCubic_write(PathStrokeCubicRef(path_out_ref.offset + 4), path_cubic);
break;
case Element_FillCubic:
case Element_StrokeCubic:
CubicSeg cubic = Element_StrokeCubic_read(this_ref);
PathStrokeCubic path_cubic;
path_cubic;
path_cubic.p0 = st.mat.xy * cubic.p0.x + st.mat.zw * cubic.p0.y + st.translate;
path_cubic.p1 = st.mat.xy * cubic.p1.x + st.mat.zw * cubic.p1.y + st.translate;
path_cubic.p1 = st.mat.xy * cubic.p2.x + st.mat.zw * cubic.p2.y + st.translate;
path_cubic.p1 = st.mat.xy * cubic.p3.x + st.mat.zw * cubic.p3.y + st.translate;
path_cubic.p2 = st.mat.xy * cubic.p2.x + st.mat.zw * cubic.p2.y + st.translate;
path_cubic.p3 = st.mat.xy * cubic.p3.x + st.mat.zw * cubic.p3.y + st.translate;
path_cubic.path_ix = st.path_count;
if (tag == Element_StrokeCubic) {
path_cubic.stroke = get_linewidth(st);
@ -350,7 +355,7 @@ void main() {
// We do encoding a bit by hand to minimize divergence. Another approach
// would be to have a fill/stroke bool.
path_out_ref = PathSegRef((st.pathseg_count - 1) * PathSeg_size);
out_tag = tag == Element_FillLine ? PathSeg_FillCubic : PathSeg_StrokeCubic;
out_tag = tag == Element_FillCubic ? PathSeg_FillCubic : PathSeg_StrokeCubic;
pathseg[path_out_ref.offset >> 2] = out_tag;
PathStrokeCubic_write(PathStrokeCubicRef(path_out_ref.offset + 4), path_cubic);
break;

BIN
piet-gpu/shader/elements.spv
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158
piet-gpu/shader/path_coarse.comp
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@ -33,6 +33,14 @@ layout(set = 0, binding = 2) buffer TileBuf {
#define SX (1.0 / float(TILE_WIDTH_PX))
#define SY (1.0 / float(TILE_HEIGHT_PX))
#define Q_ACCURACY 0.025
#define MAX_HYPOT2 (432.0 * Q_ACCURACY * Q_ACCURACY)
vec2 eval_cubic(vec2 p0, vec2 p1, vec2 p2, vec2 p3, float t) {
float mt = 1.0 - t;
return p0 * (mt * mt * mt) + (p1 * (mt * mt * 3.0) + (p2 * (mt * 3.0) + p3 * t) * t) * t;
}
void main() {
uint element_ix = gl_GlobalInvocationID.x;
PathSegRef ref = PathSegRef(element_ix * PathSeg_size);
@ -48,6 +56,7 @@ void main() {
PathStrokeLine line;
float dx;
switch (tag) {
/*
case PathSeg_FillLine:
case PathSeg_StrokeLine:
line = PathSeg_StrokeLine_read(ref);
@ -63,66 +72,101 @@ void main() {
b = invslope; // Note: assumes square tiles, otherwise scale.
a = (line.p0.x - (line.p0.y - 0.5 * float(TILE_HEIGHT_PX)) * b) * SX;
break;
}
int x0 = int(floor((xmin) * SX));
int x1 = int(ceil((xmax) * SX));
int y0 = int(floor((ymin) * SY));
int y1 = int(ceil((ymax) * SY));
uint path_ix = line.path_ix;
Path path = Path_read(PathRef(path_ix * Path_size));
ivec4 bbox = ivec4(path.bbox);
x0 = clamp(x0, bbox.x, bbox.z);
y0 = clamp(y0, bbox.y, bbox.w);
x1 = clamp(x1, bbox.x, bbox.z);
y1 = clamp(y1, bbox.y, bbox.w);
float t = a + b * float(y0);
int stride = bbox.z - bbox.x;
int base = (y0 - bbox.y) * stride - bbox.x;
// TODO: can be tighter, use c to bound width
uint n_tile_alloc = uint((x1 - x0) * (y1 - y0));
// Consider using subgroups to aggregate atomic add.
uint tile_offset = atomicAdd(alloc, n_tile_alloc * TileSeg_size);
TileSeg tile_seg;
for (int y = y0; y < y1; y++) {
float tile_y0 = float(y * TILE_HEIGHT_PX);
if (tag == PathSeg_FillLine && min(line.p0.y, line.p1.y) <= tile_y0) {
int xray = max(int(ceil(t - 0.5 * b)), bbox.x);
if (xray < bbox.z) {
int backdrop = line.p1.y < line.p0.y ? 1 : -1;
TileRef tile_ref = Tile_index(path.tiles, uint(base + xray));
uint tile_el = tile_ref.offset >> 2;
atomicAdd(tile[tile_el + 1], backdrop);
}
}
int xx0 = clamp(int(floor(t - c)), x0, x1);
int xx1 = clamp(int(ceil(t + c)), x0, x1);
for (int x = xx0; x < xx1; x++) {
float tile_x0 = float(x * TILE_WIDTH_PX);
TileRef tile_ref = Tile_index(path.tiles, uint(base + x));
uint tile_el = tile_ref.offset >> 2;
uint old = atomicExchange(tile[tile_el], tile_offset);
tile_seg.start = line.p0;
tile_seg.end = line.p1;
float y_edge = 0.0;
if (tag == PathSeg_FillLine) {
y_edge = mix(line.p0.y, line.p1.y, (tile_x0 - line.p0.x) / dx);
if (min(line.p0.x, line.p1.x) < tile_x0 && y_edge >= tile_y0 && y_edge < tile_y0 + TILE_HEIGHT_PX) {
if (line.p0.x > line.p1.x) {
tile_seg.end = vec2(tile_x0, y_edge);
} else {
tile_seg.start = vec2(tile_x0, y_edge);
*/
case PathSeg_FillCubic:
case PathSeg_StrokeCubic:
PathStrokeCubic cubic = PathSeg_StrokeCubic_read(ref);
vec2 err_v = 3.0 * (cubic.p2 - cubic.p1) + cubic.p0 - cubic.p3;
float err = err_v.x * err_v.x + err_v.y * err_v.y;
// The number of quadratics.
uint n = max(uint(ceil(pow(err * (1.0 / MAX_HYPOT2), 1.0 / 6.0))), 1);
vec2 p0 = cubic.p0;
float step = 1.0 / float(n);
uint path_ix = cubic.path_ix;
Path path = Path_read(PathRef(path_ix * Path_size));
ivec4 bbox = ivec4(path.bbox);
for (int i = 0; i < n; i++) {
// TODO: probably need special logic to make sure it's manifold
float t = float(i + 1) * step;
vec2 p2 = eval_cubic(cubic.p0, cubic.p1, cubic.p2, cubic.p3, t);
/*
vec2 p1 = eval_cubic(cubic.p0, cubic.p1, cubic.p2, cubic.p3, t - 0.5 * step);
p1 = 2.0 * p1 - 0.5 * (p0 + p2);
*/
xmin = min(p0.x, p2.x) - cubic.stroke.x;
xmax = max(p0.x, p2.x) + cubic.stroke.x;
ymin = min(p0.y, p2.y) - cubic.stroke.y;
ymax = max(p0.y, p2.y) + cubic.stroke.y;
float dx = p2.x - p0.x;
float dy = p2.y - p0.y;
// Set up for per-scanline coverage formula, below.
float invslope = abs(dy) < 1e-9 ? 1e9 : dx / dy;
c = (cubic.stroke.x + abs(invslope) * (0.5 * float(TILE_HEIGHT_PX) + cubic.stroke.y)) * SX;
b = invslope; // Note: assumes square tiles, otherwise scale.
a = (p0.x - (p0.y - 0.5 * float(TILE_HEIGHT_PX)) * b) * SX;
int x0 = int(floor((xmin) * SX));
int x1 = int(ceil((xmax) * SX));
int y0 = int(floor((ymin) * SY));
int y1 = int(ceil((ymax) * SY));
x0 = clamp(x0, bbox.x, bbox.z);
y0 = clamp(y0, bbox.y, bbox.w);
x1 = clamp(x1, bbox.x, bbox.z);
y1 = clamp(y1, bbox.y, bbox.w);
float xc = a + b * float(y0);
int stride = bbox.z - bbox.x;
int base = (y0 - bbox.y) * stride - bbox.x;
// TODO: can be tighter, use c to bound width
uint n_tile_alloc = uint((x1 - x0) * (y1 - y0));
// Consider using subgroups to aggregate atomic add.
uint tile_offset = atomicAdd(alloc, n_tile_alloc * TileSeg_size);
TileSeg tile_seg;
for (int y = y0; y < y1; y++) {
float tile_y0 = float(y * TILE_HEIGHT_PX);
if (tag == PathSeg_FillCubic && min(p0.y, p2.y) <= tile_y0) {
int xray = max(int(ceil(xc - 0.5 * b)), bbox.x);
if (xray < bbox.z) {
int backdrop = p2.y < p0.y ? 1 : -1;
TileRef tile_ref = Tile_index(path.tiles, uint(base + xray));
uint tile_el = tile_ref.offset >> 2;
atomicAdd(tile[tile_el + 1], backdrop);
}
} else {
y_edge = 1e9;
}
int xx0 = clamp(int(floor(xc - c)), x0, x1);
int xx1 = clamp(int(ceil(xc + c)), x0, x1);
for (int x = xx0; x < xx1; x++) {
float tile_x0 = float(x * TILE_WIDTH_PX);
TileRef tile_ref = Tile_index(path.tiles, uint(base + x));
uint tile_el = tile_ref.offset >> 2;
uint old = atomicExchange(tile[tile_el], tile_offset);
tile_seg.start = p0;
tile_seg.end = p2;
float y_edge = 0.0;
if (tag == PathSeg_FillCubic) {
y_edge = mix(p0.y, p2.y, (tile_x0 - p0.x) / dx);
if (min(p0.x, p2.x) < tile_x0 && y_edge >= tile_y0 && y_edge < tile_y0 + TILE_HEIGHT_PX) {
if (p0.x > p2.x) {
tile_seg.end = vec2(tile_x0, y_edge);
} else {
tile_seg.start = vec2(tile_x0, y_edge);
}
} else {
y_edge = 1e9;
}
}
tile_seg.y_edge = y_edge;
tile_seg.next.offset = old;
TileSeg_write(TileSegRef(tile_offset), tile_seg);
tile_offset += TileSeg_size;
}
xc += b;
base += stride;
}
tile_seg.y_edge = y_edge;
tile_seg.next.offset = old;
TileSeg_write(TileSegRef(tile_offset), tile_seg);
tile_offset += TileSeg_size;
p0 = p2;
}
t += b;
base += stride;
break;
}
}

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piet-gpu/shader/path_coarse.spv
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2
piet-gpu/src/render_ctx.rs
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@ -242,7 +242,7 @@ impl PietGpuRenderContext {
}
fn encode_path(&mut self, path: impl Iterator<Item = PathEl>, is_fill: bool) {
let flatten = true;
let flatten = false;
if flatten {
let mut start_pt = None;
let mut last_pt = None;