108 lines
3.1 KiB
GLSL
108 lines
3.1 KiB
GLSL
// VERTEX_SHADER
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// linear_gradient.glsl
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uniform vec4 u_points;
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_OUT_ vec4 info;
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void main() {
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gl_Position = u_projection * (u_modelview * vec4(aPosition, 0.0, 1.0));
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vec2 mv0 = u_modelview[0].xy;
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vec2 mv1 = u_modelview[1].xy;
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vec2 offset = aPosition - u_points.xy;
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vec2 coord = vec2(dot(mv0, offset),
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dot(mv1, offset));
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// Original equation:
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// VS | maxDist = length(end - start);
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// VS | gradient = end - start;
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// VS | gradientLength = length(gradient);
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// FS | pos = frag_coord - start
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// FS | proj = (dot(gradient, pos) / (gradientLength * gradientLength)) * gradient
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// FS | offset = length(proj) / maxDist
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// Simplified formula derivation:
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// 1. Notice that maxDist = gradientLength:
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// offset = length(proj) / gradientLength
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// 2. Let gnorm = gradient / gradientLength, then:
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// proj = (dot(gnorm * gradientLength, pos) / (gradientLength * gradientLength)) * (gnorm * gradientLength) =
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// = dot(gnorm, pos) * gnorm
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// 3. Since gnorm is unit length then:
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// length(proj) = length(dot(gnorm, pos) * gnorm) = dot(gnorm, pos)
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// 4. We can avoid the FS division by passing a scaled pos from the VS:
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// offset = dot(gnorm, pos) / gradientLength = dot(gnorm, pos / gradientLength)
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// 5. 1.0 / length(gradient) is inversesqrt(dot(gradient, gradient)) in GLSL
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vec2 gradient = vec2(dot(mv0, u_points.zw),
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dot(mv1, u_points.zw));
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float rcp_gradient_length = inversesqrt(dot(gradient, gradient));
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info = rcp_gradient_length * vec4(coord, gradient);
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}
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// FRAGMENT_SHADER:
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// linear_gradient.glsl
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#define MAX_COLOR_STOPS 6
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#ifdef GSK_LEGACY
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uniform int u_num_color_stops;
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#else
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uniform highp int u_num_color_stops; // Why? Because it works like this.
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#endif
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uniform float u_color_stops[MAX_COLOR_STOPS * 5];
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uniform bool u_repeat;
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_IN_ vec4 info;
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float get_offset(int index) {
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// u_color_stops[5 * index] makes Intel Windows driver crash.
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// See https://gitlab.gnome.org/GNOME/gtk/-/issues/3783
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int base = 5 * index;
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return u_color_stops[base];
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}
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vec4 get_color(int index) {
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int base = 5 * index + 1;
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return vec4(u_color_stops[base],
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u_color_stops[base + 1],
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u_color_stops[base + 2],
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u_color_stops[base + 3]);
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}
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void main() {
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float offset = dot(info.xy, info.zw);
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float curr_offset;
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float next_offset;
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if (u_repeat) {
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offset = fract(offset);
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}
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next_offset = get_offset(0);
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if (offset < next_offset) {
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gskSetOutputColor(gsk_scaled_premultiply(get_color(0), u_alpha));
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return;
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}
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if (offset >= get_offset(u_num_color_stops - 1)) {
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gskSetOutputColor(gsk_scaled_premultiply(get_color(u_num_color_stops - 1), u_alpha));
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return;
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}
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for (int i = 0; i < MAX_COLOR_STOPS; i++) {
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curr_offset = next_offset;
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next_offset = get_offset(i + 1);
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if (offset < next_offset) {
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float f = (offset - curr_offset) / (next_offset - curr_offset);
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vec4 curr_color = get_color(i);
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vec4 next_color = get_color(i + 1);
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vec4 color = mix(curr_color, next_color, f);
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gskSetScaledOutputColor(gsk_premultiply (color), u_alpha);
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return;
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}
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}
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}
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