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// Copyright 2017 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
precision mediump float;
// A rounded rect is represented by a vec4 specifying (min.xy, max.xy)
// and a matrix of corners. Each vector in the matrix represents a corner
// (order: top left, top right, bottom left, bottom right). Each corner vec4
// represents (start.xy, radius.xy).
uniform vec4 u_scissor_rect;
uniform mat4 u_scissor_corners;
uniform vec4 u_spread_rect;
uniform mat4 u_spread_corners;
// The scale_add uniform is used to switch the shader between generating
// outset shadows and inset shadows. It impacts the shadow gradient and
// scissor behavior. Use (1, 0) to get an outset shadow with the provided
// scissor rect behaving as an exclusive scissor, and (-1, 1) to get an
// inset shadow with scissor rect behaving as an inclusive scissor.
uniform vec2 u_scale_add;
// Blur calculations happen in terms in sigma distances. Use sigma_scale to
// translate pixel distances into sigma distances.
uniform vec2 u_sigma_scale;
// Adjust the sigma input value to tweak the blur output so that it better
// matches the reference. This is usually only needed for very large sigmas.
uniform vec2 u_sigma_tweak;
varying vec2 v_offset;
varying vec4 v_color;
// Return 0 if the current point is inside the rounded rect, or scale towards 1
// as it goes outside a 1-pixel anti-aliasing border.
float GetRRectScale(vec4 rect, mat4 corners) {
vec4 select_corner = vec4(
step(v_offset.x, corners[0].x) * step(v_offset.y, corners[0].y),
step(corners[1].x, v_offset.x) * step(v_offset.y, corners[1].y),
step(v_offset.x, corners[2].x) * step(corners[2].y, v_offset.y),
step(corners[3].x, v_offset.x) * step(corners[3].y, v_offset.y));
if (dot(select_corner, vec4(1.0)) > 0.5) {
// Estimate the amount of anti-aliasing that should be used by comparing
// x^2 / a^2 + y^2 / b^2 for the ellipse and ellipse + 1 pixel.
vec4 corner = corners * select_corner;
vec2 pixel_offset = v_offset - corner.xy;
if (corner.z * corner.w < 0.1) {
// This is a square corner.
return min(length(pixel_offset), 1.0);
}
vec2 offset_min = pixel_offset / corner.zw;
vec2 offset_max = pixel_offset / (corner.zw + vec2(1.0));
float result_min = dot(offset_min, offset_min);
float result_max = dot(offset_max, offset_max);
// Return 1.0 if outside, or interpolate if in the border, or 0 if inside.
return (result_max >= 1.0) ? 1.0 :
max(result_min - 1.0, 0.0) / (result_min - result_max);
}
return clamp(rect.x - v_offset.x, 0.0, 1.0) +
clamp(v_offset.x - rect.z, 0.0, 1.0) +
clamp(rect.y - v_offset.y, 0.0, 1.0) +
clamp(v_offset.y - rect.w, 0.0, 1.0);
}
// Calculate the distance from a point in the first quadrant to an ellipse
// centered at the origin.
//
// http://iquilezles.org/www/articles/ellipsedist/ellipsedist.htm
float GetEllipseDistance(vec2 p, vec2 ab) {
if (abs(ab.x - ab.y) < 0.5) {
return length(p) - ab.x;
}
if (p.x > p.y) {
p = p.yx;
ab = ab.yx;
}
float lr = 1.0 / (ab.y * ab.y - ab.x * ab.x);
float m = ab.x * p.x * lr;
float m2 = m * m;
float n = ab.y * p.y * lr;
float n2 = n * n;
float c = (m2 + n2 - 1.0) * 0.333333333;
float c3 = c * c * c;
float q = c3 + m2 * n2 * 2.0;
float d = c3 + m2 * n2;
float g = m + m * n2;
float co;
if (d < 0.0) {
float p = acos(q / c3) * 0.333333333;
float s = cos(p);
float t = sin(p) * 1.732050808;
float rx = sqrt(-c * (s + t + 2.0) + m2);
float ry = sqrt(-c * (s - t + 2.0) + m2);
co = (ry + sign(lr) * rx + abs(g) / (rx * ry) - m) * 0.5;
} else {
float h = 2.0 * m * n * sqrt(d);
float s = sign(q + h) * pow(abs(q + h), 0.333333333);
float u = sign(q - h) * pow(abs(q - h), 0.333333333);
float rx = -s - u - c * 4.0 + 2.0 * m2;
float ry = (s - u) * 1.732050808;
float rm = sqrt(rx * rx + ry * ry);
float p = ry / sqrt(rm - rx);
co = (p + 2.0 * g / rm - m) * 0.5;
}
float si = sqrt(1.0 - co * co);
vec2 closest = vec2(ab.x * co, ab.y * si);
return length(closest - p) * sign(p.y - closest.y);
}
// Get the x and y distances from the nearest edges of the rounded rect.
vec2 GetBlurPosition(vec4 rect, mat4 corners) {
vec2 pos = max(rect.xy - v_offset, v_offset - rect.zw);
vec4 select_corner = vec4(
step(v_offset.x, corners[0].x) * step(v_offset.y, corners[0].y),
step(corners[1].x, v_offset.x) * step(v_offset.y, corners[1].y),
step(v_offset.x, corners[2].x) * step(corners[2].y, v_offset.y),
step(corners[3].x, v_offset.x) * step(corners[3].y, v_offset.y));
if (dot(select_corner, vec4(1.0)) > 0.5) {
// Use distance from the closest point on the ellipse as the position
// for blur calculations.
vec4 corner = corners * select_corner;
float dist = GetEllipseDistance(abs(v_offset - corner.xy), corner.zw);
// Since the transition from non-corner to corner positions happens along
// the ellipse's x or y axis, either pos.x = -corner.z or pos.y = -corner.w
// when the transition happens. Keep one ordinate at a minimum so that
// distance from the ellipse smoothly changes blur intensity.
//
// The return vec2 is used as blur = gi(x) * gi(y) where gi = the guassian
// integral function. Swapping x and y has no impact on the final blur, so
// distance can be substituted for one ordinate as long as the other takes
// the right value. E.g. when pos = (-corner.z, 0), the point is on the top
// center of the ellipse, so dist = 0. When pos = (0, -corner.w), dist = 0.
// When pos = (-corner.z, -corner.w), the point is at the center of the
// ellipse, and dist = max(-corner.z, -corner.w). So dist can be used as
// long as the other ordinate is min(pos.x, pos.y).
return vec2(dist, min(min(pos.x, pos.y), max(-corner.z, -corner.w)));
}
return pos;
}
void main() {
float scissor_scale = GetRRectScale(u_scissor_rect, u_scissor_corners) *
u_scale_add.x + u_scale_add.y;
vec2 pos = GetBlurPosition(u_spread_rect, u_spread_corners) *
u_sigma_scale + u_sigma_tweak;
vec2 pos2 = pos * pos;
vec2 pos3 = pos2 * pos;
vec4 posx = vec4(1.0, pos.x, pos2.x, pos3.x);
vec4 posy = vec4(1.0, pos.y, pos2.y, pos3.y);
// Approximation of the gaussian integral from [x, +inf).
// http://stereopsis.com/shadowrect/
const vec4 klower = vec4(0.4375, -1.125, -0.75, -0.1666666);
const vec4 kmiddle = vec4(0.5, -0.75, 0.0, 0.3333333);
const vec4 kupper = vec4(0.5625, -1.125, 0.75, -0.1666666);
float gaussx = 0.0;
if (pos.x < -1.5) {
gaussx = 1.0;
} else if (pos.x < -0.5) {
gaussx = dot(posx, klower);
} else if (pos.x < 0.5) {
gaussx = dot(posx, kmiddle);
} else if (pos.x < 1.5) {
gaussx = dot(posx, kupper);
}
float gaussy = 0.0;
if (pos.y < -1.5) {
gaussy = 1.0;
} else if (pos.y < -0.5) {
gaussy = dot(posy, klower);
} else if (pos.y < 0.5) {
gaussy = dot(posy, kmiddle);
} else if (pos.y < 1.5) {
gaussy = dot(posy, kupper);
}
float alpha_scale = gaussx * gaussy * u_scale_add.x + u_scale_add.y;
gl_FragColor = v_color * (alpha_scale * scissor_scale);
}