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gpu: [compute] fix path gaps by eliminating redundant path points

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See https://github.com/linebender/piet-gpu/issues/62 for description
of the issue. The fix is the Gio copy of the piet-gpu fix.

Signed-off-by: Elias Naur <mail@eliasnaur.com>
This commit is contained in:
Elias Naur
2021-02-15 20:04:01 +01:00
parent b5d21b209c
commit 2feec23561
6 changed files with 105 additions and 158 deletions
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gpu/shaders/path_coarse.comp
+16 -6
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@@ -86,6 +86,14 @@ SubdivResult estimate_subdiv(vec2 p0, vec2 p1, vec2 p2, float sqrt_tol) {
return SubdivResult(val, a0, a2);
}
// PathSeg_Cubic_read_p0 is like PathSeg_StrokeCubic_read except it only reads p0.
vec2 PathSeg_Cubic_read_p0(Alloc a, PathSegRef ref) {
uint ix = (ref.offset + 4) >> 2;
uint raw0 = read_mem(a, ix + 0);
uint raw1 = read_mem(a, ix + 1);
return vec2(uintBitsToFloat(raw0), uintBitsToFloat(raw1));
}
void main() {
if (mem_error != NO_ERROR) {
return;
@@ -102,7 +110,9 @@ void main() {
case PathSeg_FillCubic:
case PathSeg_StrokeCubic:
PathStrokeCubic cubic = PathSeg_StrokeCubic_read(conf.pathseg_alloc, ref);
vec2 err_v = 3.0 * (cubic.p2 - cubic.p1) + cubic.p0 - cubic.p3;
PathSegRef succ_ref = PathSegRef(conf.pathseg_alloc.offset + cubic.succ_ix * PathSeg_size);
vec2 p3 = PathSeg_Cubic_read_p0(conf.pathseg_alloc, succ_ref);
vec2 err_v = 3.0 * (cubic.p2 - cubic.p1) + cubic.p0 - p3;
float err = err_v.x * err_v.x + err_v.y * err_v.y;
// The number of quadratics.
uint n_quads = max(uint(ceil(pow(err * (1.0 / MAX_HYPOT2), 1.0 / 6.0))), 1);
@@ -112,8 +122,8 @@ void main() {
float step = 1.0 / float(n_quads);
for (uint i = 0; i < n_quads; i++) {
float t = float(i + 1) * step;
vec2 qp2 = eval_cubic(cubic.p0, cubic.p1, cubic.p2, cubic.p3, t);
vec2 qp1 = eval_cubic(cubic.p0, cubic.p1, cubic.p2, cubic.p3, t - 0.5 * step);
vec2 qp2 = eval_cubic(cubic.p0, cubic.p1, cubic.p2, p3, t);
vec2 qp1 = eval_cubic(cubic.p0, cubic.p1, cubic.p2, p3, t - 0.5 * step);
qp1 = 2.0 * qp1 - 0.5 * (qp0 + qp2);
SubdivResult params = estimate_subdiv(qp0, qp1, qp2, sqrt(REM_ACCURACY));
val += params.val;
@@ -133,8 +143,8 @@ void main() {
float val_sum = 0.0;
for (uint i = 0; i < n_quads; i++) {
float t = float(i + 1) * step;
vec2 qp2 = eval_cubic(cubic.p0, cubic.p1, cubic.p2, cubic.p3, t);
vec2 qp1 = eval_cubic(cubic.p0, cubic.p1, cubic.p2, cubic.p3, t - 0.5 * step);
vec2 qp2 = eval_cubic(cubic.p0, cubic.p1, cubic.p2, p3, t);
vec2 qp1 = eval_cubic(cubic.p0, cubic.p1, cubic.p2, p3, t - 0.5 * step);
qp1 = 2.0 * qp1 - 0.5 * (qp0 + qp2);
SubdivResult params = estimate_subdiv(qp0, qp1, qp2, sqrt(REM_ACCURACY));
float u0 = approx_parabola_inv_integral(params.a0);
@@ -144,7 +154,7 @@ void main() {
while (n_out == n || target < val_sum + params.val) {
vec2 p1;
if (n_out == n) {
p1 = cubic.p3;
p1 = p3;
} else {
float u = (target - val_sum) / params.val;
float a = mix(params.a0, params.a2, u);