зеркало из https://github.com/mozilla/gecko-dev.git
96 строки
3.7 KiB
GLSL
96 строки
3.7 KiB
GLSL
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#define EPSILON 0.0001
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flat varying vec4 vTransformBounds;
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#ifdef WR_VERTEX_SHADER
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void init_transform_vs(vec4 local_bounds) {
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vTransformBounds = local_bounds;
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}
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#endif //WR_VERTEX_SHADER
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#ifdef WR_FRAGMENT_SHADER
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/// Find the appropriate half range to apply the AA approximation over.
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/// This range represents a coefficient to go from one CSS pixel to half a device pixel.
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float compute_aa_range(vec2 position) {
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// The constant factor is chosen to compensate for the fact that length(fw) is equal
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// to sqrt(2) times the device pixel ratio in the typical case. 0.5/sqrt(2) = 0.35355.
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//
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// This coefficient is chosen to ensure that any sample 0.5 pixels or more inside of
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// the shape has no anti-aliasing applied to it (since pixels are sampled at their center,
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// such a pixel (axis aligned) is fully inside the border). We need this so that antialiased
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// curves properly connect with non-antialiased vertical or horizontal lines, among other things.
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//
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// Lines over a half-pixel away from the pixel center *can* intersect with the pixel square;
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// indeed, unless they are horizontal or vertical, they are guaranteed to. However, choosing
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// a nonzero area for such pixels causes noticeable artifacts at the junction between an anti-
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// aliased corner and a straight edge.
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//
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// We may want to adjust this constant in specific scenarios (for example keep the principled
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// value for straight edges where we want pixel-perfect equivalence with non antialiased lines
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// when axis aligned, while selecting a larger and smoother aa range on curves).
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return 0.35355 * length(fwidth(position));
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}
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/// Return the blending coefficient for distance antialiasing.
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///
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/// 0.0 means inside the shape, 1.0 means outside.
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///
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/// This cubic polynomial approximates the area of a 1x1 pixel square under a
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/// line, given the signed Euclidean distance from the center of the square to
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/// that line. Calculating the *exact* area would require taking into account
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/// not only this distance but also the angle of the line. However, in
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/// practice, this complexity is not required, as the area is roughly the same
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/// regardless of the angle.
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///
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/// The coefficients of this polynomial were determined through least-squares
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/// regression and are accurate to within 2.16% of the total area of the pixel
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/// square 95% of the time, with a maximum error of 3.53%.
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///
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/// See the comments in `compute_aa_range()` for more information on the
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/// cutoff values of -0.5 and 0.5.
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float distance_aa(float aa_range, float signed_distance) {
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float dist = 0.5 * signed_distance / aa_range;
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if (dist <= -0.5 + EPSILON)
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return 1.0;
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if (dist >= 0.5 - EPSILON)
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return 0.0;
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return 0.5 + dist * (0.8431027 * dist * dist - 1.14453603);
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}
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float signed_distance_rect(vec2 pos, vec2 p0, vec2 p1) {
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vec2 d = max(p0 - pos, pos - p1);
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return length(max(vec2(0.0), d)) + min(0.0, max(d.x, d.y));
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}
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float init_transform_fs(vec2 local_pos) {
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// Get signed distance from local rect bounds.
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float d = signed_distance_rect(
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local_pos,
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vTransformBounds.xy,
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vTransformBounds.zw
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);
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// Find the appropriate distance to apply the AA smoothstep over.
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float aa_range = compute_aa_range(local_pos);
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// Only apply AA to fragments outside the signed distance field.
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return distance_aa(aa_range, d);
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}
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float init_transform_rough_fs(vec2 local_pos) {
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return point_inside_rect(
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local_pos,
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vTransformBounds.xy,
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vTransformBounds.zw
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);
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}
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#endif //WR_FRAGMENT_SHADER
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