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Address review feedback

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* replace one_minus_focal_x and abs_one_minus_focal_x variables with the actual expressions
* replace division by r^2-1 with multiplication by reciprocal
* revert chain selects to branchy code for clarity. Branching is dynamically uniform so shouldn't affect performance
* add suggested comment describing gradient kind/flags constants
This commit is contained in:
Chad Brokaw 2023-05-15 14:45:38 -04:00
parent 5e1188f968
commit 58c7df469d
3 changed files with 42 additions and 94 deletions
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11
shader/draw_leaf.wgsl
View file

@ -184,9 +184,7 @@ fn main(
r1 = tmp_r; r1 = tmp_r;
} }
focal_x = r0 / (r0 - r1); focal_x = r0 / (r0 - r1);
let one_minus_focal_x = 1.0 - focal_x; let cf = (1.0 - focal_x) * p0 + focal_x * p1;
let cf = one_minus_focal_x * p0 + focal_x * p1;
let abs_one_minus_focal_x = abs(one_minus_focal_x);
radius = r1 / (distance(cf, p1)); radius = r1 / (distance(cf, p1));
let user_to_unit_line = transform_mul( let user_to_unit_line = transform_mul(
two_point_to_unit_line(cf, p1), two_point_to_unit_line(cf, p1),
@ -196,15 +194,16 @@ fn main(
// When r == 1.0, focal point is on circle // When r == 1.0, focal point is on circle
if abs(radius - 1.0) <= GRADIENT_EPSILON { if abs(radius - 1.0) <= GRADIENT_EPSILON {
kind = RAD_GRAD_KIND_FOCAL_ON_CIRCLE; kind = RAD_GRAD_KIND_FOCAL_ON_CIRCLE;
let scale = 0.5 * abs_one_minus_focal_x; let scale = 0.5 * abs(1.0 - focal_x);
user_to_scaled = transform_mul( user_to_scaled = transform_mul(
Transform(vec4(scale, 0.0, 0.0, scale), vec2(0.0)), Transform(vec4(scale, 0.0, 0.0, scale), vec2(0.0)),
user_to_unit_line user_to_unit_line
); );
} else { } else {
let a = radius * radius - 1.0; let a = radius * radius - 1.0;
let scale_x = radius / a * abs_one_minus_focal_x; let a_recip = 1.0 / a;
let scale_y = sqrt(abs(a)) / a * abs_one_minus_focal_x; let scale_x = radius * a_recip * abs(1.0 - focal_x);
let scale_y = sqrt(abs(a)) * a_recip * abs(1.0 - focal_x);
user_to_scaled = transform_mul( user_to_scaled = transform_mul(
Transform(vec4(scale_x, 0.0, 0.0, scale_y), vec2(0.0)), Transform(vec4(scale_x, 0.0, 0.0, scale_y), vec2(0.0)),
user_to_unit_line user_to_unit_line

121
shader/fine.wgsl
View file

@ -118,30 +118,20 @@ fn extend_mode(t: f32, mode: u32) -> f32 {
let EXTEND_PAD = 0u; let EXTEND_PAD = 0u;
let EXTEND_REPEAT = 1u; let EXTEND_REPEAT = 1u;
let EXTEND_REFLECT = 2u; let EXTEND_REFLECT = 2u;
// Branching version of the code below: switch mode {
// // EXTEND_PAD
// switch mode { case 0u: {
// // EXTEND_PAD return clamp(t, 0.0, 1.0);
// case 0u: { }
// return clamp(t, 0.0, 1.0); // EXTEND_REPEAT
// } case 1u: {
// // EXTEND_REPEAT return fract(t);
// case 1u: { }
// return fract(t); // EXTEND_REFLECT
// } default: {
// // EXTEND_REFLECT return abs(t - 2.0 * round(0.5 * t));
// default: { }
// return abs(t - 2.0 * round(0.5 * t)); }
// }
// }
let pad = clamp(t, 0.0, 1.0);
let repeat = fract(t);
let reflect = abs(t - 2.0 * round(0.5 * t));
return select(
select(pad, repeat, mode == EXTEND_REPEAT),
reflect,
mode == EXTEND_REFLECT
);
} }
#else #else
@ -309,16 +299,14 @@ fn main(
case 7u: { case 7u: {
let rad = read_rad_grad(cmd_ix); let rad = read_rad_grad(cmd_ix);
let focal_x = rad.focal_x; let focal_x = rad.focal_x;
let one_minus_focal_x = 1.0 - focal_x;
let radius = rad.radius; let radius = rad.radius;
let is_strip = rad.kind == RAD_GRAD_KIND_STRIP; let is_strip = rad.kind == RAD_GRAD_KIND_STRIP;
let is_circular = rad.kind == RAD_GRAD_KIND_CIRCULAR; let is_circular = rad.kind == RAD_GRAD_KIND_CIRCULAR;
let is_focal_on_circle = rad.kind == RAD_GRAD_KIND_FOCAL_ON_CIRCLE; let is_focal_on_circle = rad.kind == RAD_GRAD_KIND_FOCAL_ON_CIRCLE;
let is_swapped = (rad.flags & RAD_GRAD_SWAPPED) != 0u; let is_swapped = (rad.flags & RAD_GRAD_SWAPPED) != 0u;
let is_greater = radius > 1.0; let r1_recip = select(1.0 / radius, 0.0, is_circular);
let inv_r1 = select(1.0 / radius, 0.0, is_circular); let less_scale = select(1.0, -1.0, is_swapped || (1.0 - focal_x) < 0.0);
let less_scale = select(1.0, -1.0, is_swapped || one_minus_focal_x < 0.0); let t_sign = sign(1.0 - focal_x);
let t_sign = sign(one_minus_focal_x);
for (var i = 0u; i < PIXELS_PER_THREAD; i += 1u) { for (var i = 0u; i < PIXELS_PER_THREAD; i += 1u) {
let my_xy = vec2(xy.x + f32(i), xy.y); let my_xy = vec2(xy.x + f32(i), xy.y);
let local_xy = rad.matrx.xy * my_xy.x + rad.matrx.zw * my_xy.y + rad.xlat; let local_xy = rad.matrx.xy * my_xy.x + rad.matrx.zw * my_xy.y + rad.xlat;
@ -326,65 +314,22 @@ fn main(
let y = local_xy.y; let y = local_xy.y;
let xx = x * x; let xx = x * x;
let yy = y * y; let yy = y * y;
let x_inv_r1 = x * inv_r1; var t = 0.0;
// This is the branching version of the code implemented var is_valid = true;
// by the chained selects below: if is_strip {
// let a = radius - yy;
// var t = 0.0; t = sqrt(a) + x;
// var is_valid = true; is_valid = a >= 0.0;
// if is_strip { } else if is_focal_on_circle {
// let a = radius - yy; t = (xx + yy) / x;
// t = sqrt(a) + x; is_valid = t >= 0.0 && x != 0.0;
// is_valid = a >= 0.0; } else if radius > 1.0 {
// } else if is_focal_on_circle { t = sqrt(xx + yy) - x * r1_recip;
// t = (xx + yy) / x; } else { // radius < 1.0
// is_valid = t >= 0.0; let a = xx - yy;
// } else if radius > 1.0 { t = less_scale * sqrt(a) - x * r1_recip;
// t = sqrt(xx + yy) - x_inv_r1; is_valid = a >= 0.0 && t >= 0.0;
// } else { }
// let a = xx - yy;
// t = root_f * sqrt(a) - x_inv_r1;
// is_valid = a >= 0.0 && t >= 0.0;
// }
//
// The pattern is that these can all be computed with
// the expression: a * sqrt(b) + c
//
// The parameters to the expression are computed up front
// and chosen with chained selects based on their
// respective conditions. The same process is done
// for determining the validity of the resulting value.
var strip_params = vec3(1.0, radius - yy, x);
var foc_params = vec3(1.0, 0.0, (xx + yy) / x);
var greater_params = vec3(1.0, xx + yy, -x_inv_r1);
var less_params = vec3(less_scale, xx - yy, -x_inv_r1);
var params = select(
select(
select(
less_params,
greater_params,
is_greater,
),
foc_params,
is_focal_on_circle,
),
strip_params,
is_strip,
);
var t = params.x * sqrt(params.y) + params.z;
let is_valid = select(
select(
select(
params.y >= 0.0 && t >= 0.0,
true,
is_greater
),
t >= 0.0 && x != 0.0,
is_focal_on_circle,
),
params.y >= 0.0,
is_strip,
);
if is_valid { if is_valid {
t = extend_mode(focal_x + t_sign * t, rad.extend_mode); t = extend_mode(focal_x + t_sign * t, rad.extend_mode);
t = select(t, 1.0 - t, is_swapped); t = select(t, 1.0 - t, is_swapped);

4
shader/shared/config.wgsl
View file

@ -50,6 +50,10 @@ let N_TILE = 256u;
let BLEND_STACK_SPLIT = 4u; let BLEND_STACK_SPLIT = 4u;
// The following are computed in draw_leaf from the generic gradient parameters
// encoded in the scene, and stored in the gradient's info struct, for
// consumption during fine rasterization.
// Radial gradient kinds // Radial gradient kinds
let RAD_GRAD_KIND_CIRCULAR = 1u; let RAD_GRAD_KIND_CIRCULAR = 1u;
let RAD_GRAD_KIND_STRIP = 2u; let RAD_GRAD_KIND_STRIP = 2u;