impeller/entity/shaders/sweep_gradient_fill.frag

// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <impeller/constants.glsl>
#include <impeller/texture.glsl>
#include <impeller/types.glsl>

uniform sampler2D texture_sampler;

uniform GradientInfo {
  vec2 center;
  float bias;
  float scale;
  float tile_mode;
  float texture_sampler_y_coord_scale;
  float alpha;
  vec2 half_texel;
}
gradient_info;

in vec2 v_position;

out vec4 frag_color;

void main() {
  vec2 coord = v_position - gradient_info.center;
  float angle = atan(-coord.y, -coord.x);

  float t =
      (angle * k1Over2Pi + 0.5 + gradient_info.bias) * gradient_info.scale;
  frag_color = IPSampleLinearWithTileMode(
      texture_sampler, vec2(t, 0.5),
      gradient_info.texture_sampler_y_coord_scale, gradient_info.half_texel,
      gradient_info.tile_mode);
  frag_color =
      vec4(frag_color.xyz * frag_color.a, frag_color.a) * gradient_info.alpha;
}