[Impeller] Optimize the calculation of interpolant value of linear gr…

…adient (#40085) [Impeller] Optimize the calculation of interpolant value of linear gradient
flutter · Mar 8, 2023 · 694a14c · 694a14c
1 parent 7684aa0
commit 694a14c
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Showing 2 changed files with 8 additions and 8 deletions.
diff --git a/impeller/entity/shaders/linear_gradient_fill.frag b/impeller/entity/shaders/linear_gradient_fill.frag
@@ -22,10 +22,10 @@ in vec2 v_position;
 out vec4 frag_color;
 
 void main() {
-  float len = length(frag_info.end_point - frag_info.start_point);
-  float dot = dot(v_position - frag_info.start_point,
-                  frag_info.end_point - frag_info.start_point);
-  float t = dot / (len * len);
+  vec2 start_to_end = frag_info.end_point - frag_info.start_point;
+  vec2 start_to_position = v_position - frag_info.start_point;
+  float t =
+      dot(start_to_position, start_to_end) / dot(start_to_end, start_to_end);
   frag_color = IPSampleLinearWithTileMode(
       texture_sampler, vec2(t, 0.5), frag_info.texture_sampler_y_coord_scale,
       frag_info.half_texel, frag_info.tile_mode);

diff --git a/impeller/entity/shaders/linear_gradient_ssbo_fill.frag b/impeller/entity/shaders/linear_gradient_ssbo_fill.frag
@@ -30,10 +30,10 @@ in vec2 v_position;
 out vec4 frag_color;
 
 void main() {
-  float len = length(frag_info.end_point - frag_info.start_point);
-  float dot = dot(v_position - frag_info.start_point,
-                  frag_info.end_point - frag_info.start_point);
-  float t = dot / (len * len);
+  vec2 start_to_end = frag_info.end_point - frag_info.start_point;
+  vec2 start_to_position = v_position - frag_info.start_point;
+  float t =
+      dot(start_to_position, start_to_end) / dot(start_to_end, start_to_end);
 
   if ((t < 0.0 || t > 1.0) && frag_info.tile_mode == kTileModeDecal) {
     frag_color = vec4(0);