From 4b1bdcce2599a471632c84ad716eaf81256f4f6c Mon Sep 17 00:00:00 2001
From: Cosma Alex Vergari <cosmavergari@gmail.com>
Date: Tue, 23 Jun 2026 11:32:37 +0200
Subject: [PATCH] fix: webgl and canvas linear gradient transparency issues

---
 src/core/shaders/canvas/LinearGradient.ts | 19 +-----
 src/core/shaders/webgl/LinearGradient.ts  | 71 +++++++----------------
 2 files changed, 22 insertions(+), 68 deletions(-)

diff --git a/src/core/shaders/canvas/LinearGradient.ts b/src/core/shaders/canvas/LinearGradient.ts
index 2cfdd36..8036d6e 100644
--- a/src/core/shaders/canvas/LinearGradient.ts
+++ b/src/core/shaders/canvas/LinearGradient.ts
@@ -31,24 +31,7 @@ export const LinearGradient: CanvasShaderType<
       y0: line * Math.sin(angle) + nHeight * 0.5,
       x1: line * Math.cos(angle + Math.PI) + nWidth * 0.5,
       y1: line * Math.sin(angle + Math.PI) + nHeight * 0.5,
-      colors: this.props!.colors.map((value, i, arr) => {
-        const alpha = (value >>> 24) & 0xff;
-        if (alpha === 0) {
-          let nearestRGB = value & 0x00ffffff;
-          for (let step = 1; step < arr.length; step++) {
-            if (i - step >= 0 && ((arr[i - step]! >>> 24) & 0xff) > 0) {
-              nearestRGB = arr[i - step]! & 0x00ffffff;
-              break;
-            }
-            if (i + step < arr.length && ((arr[i + step]! >>> 24) & 0xff) > 0) {
-              nearestRGB = arr[i + step]! & 0x00ffffff;
-              break;
-            }
-          }
-          value = (value & 0xff000000) | nearestRGB;
-        }
-        return this.toColorString(value);
-      }),
+      colors: this.props!.colors.map((value) => this.toColorString(value)),
     };
   },
   render(ctx, node, renderContext) {
diff --git a/src/core/shaders/webgl/LinearGradient.ts b/src/core/shaders/webgl/LinearGradient.ts
index c27fd15..91938ec 100644
--- a/src/core/shaders/webgl/LinearGradient.ts
+++ b/src/core/shaders/webgl/LinearGradient.ts
@@ -22,51 +22,6 @@ export const LinearGradient: WebGlShaderType<LinearGradientProps> = {
   getCacheMarkers(props: LinearGradientProps) {
     return `colors:${props.colors.length}`;
   },
-  vertex: `
-    # ifdef GL_FRAGMENT_PRECISION_HIGH
-    precision highp float;
-    # else
-    precision mediump float;
-    # endif
-
-    attribute vec2 a_position;
-    attribute vec2 a_textureCoords;
-    attribute vec4 a_color;
-
-    uniform vec2 u_resolution;
-    uniform float u_pixelRatio;
-    uniform vec2 u_dimensions;
-    uniform float u_angle;
-
-    varying vec4 v_color;
-    varying vec2 v_textureCoords;
-    varying float v_dist;
-
-    const float PI = 3.14159265359;
-
-    vec2 calcPoint(float d, float angle) {
-      return d * vec2(cos(angle), sin(angle)) + (u_dimensions * 0.5);
-    }
-
-    void main() {
-      vec2 normalized = a_position * u_pixelRatio / u_resolution;
-      vec2 zero_two = normalized * 2.0;
-      vec2 clip_space = zero_two - 1.0;
-
-      gl_Position = vec4(clip_space * vec2(1.0, -1.0), 0, 1);
-
-      v_color = a_color;
-      v_textureCoords = a_textureCoords;
-
-      float a = u_angle;
-      float lineDist = abs(u_dimensions.x * cos(a)) + abs(u_dimensions.y * sin(a));
-      vec2 f = calcPoint(lineDist * 0.5, a);
-      vec2 t = calcPoint(lineDist * 0.5, a + PI);
-      vec2 gradVec = t - f;
-      float dist = dot(a_textureCoords * u_dimensions - f, gradVec) / dot(gradVec, gradVec);
-      v_dist = dist;
-    }
-  `,
   fragment(renderer: WebGlRenderer, props: LinearGradientProps) {
     return `
     # ifdef GL_FRAGMENT_PRECISION_HIGH
@@ -75,16 +30,25 @@ export const LinearGradient: WebGlShaderType<LinearGradientProps> = {
     precision mediump float;
     # endif
 
+    #define PI 3.14159265359
     #define MAX_STOPS ${props.colors.length}
     #define LAST_STOP ${props.colors.length - 1}
 
+    uniform float u_alpha;
+    uniform vec2 u_dimensions;
+
     uniform sampler2D u_texture;
+
+    uniform float u_angle;
     uniform float u_stops[MAX_STOPS];
     uniform vec4 u_colors[MAX_STOPS];
 
     varying vec4 v_color;
     varying vec2 v_textureCoords;
-    varying float v_dist;
+
+    vec2 calcPoint(float d, float angle) {
+      return d * vec2(cos(angle), sin(angle)) + (u_dimensions * 0.5);
+    }
 
     vec4 getGradientColor(float dist) {
       dist = clamp(dist, 0.0, 1.0);
@@ -105,14 +69,21 @@ export const LinearGradient: WebGlShaderType<LinearGradientProps> = {
           return mix(u_colors[i], u_colors[i + 1], lDist);
         }
       }
-      return u_colors[LAST_STOP];
     }
 
     void main() {
       vec4 color = texture2D(u_texture, v_textureCoords) * v_color;
-      vec4 colorOut = getGradientColor(v_dist);
-      vec3 blendedRGB = mix(color.rgb, colorOut.rgb, clamp(colorOut.a, 0.0, 1.0));
-      gl_FragColor = vec4(blendedRGB, color.a);
+      float a = u_angle;
+      float lineDist = abs(u_dimensions.x * cos(a)) + abs(u_dimensions.y * sin(a));
+      vec2 f = calcPoint(lineDist * 0.5, a);
+      vec2 t = calcPoint(lineDist * 0.5, a + PI);
+      // Scale to avoid mediump float overflow on platforms without highp
+      float s = max(u_dimensions.x, u_dimensions.y);
+      vec2 gradVec = (t - f) / s;
+      float dist = dot((v_textureCoords.xy * u_dimensions - f) / s, gradVec) / dot(gradVec, gradVec);
+      vec4 colorOut = getGradientColor(dist);
+      color = mix(color, colorOut, clamp(colorOut.a, 0.0, 1.0));
+      gl_FragColor = color * u_alpha;
     }
   `;
   },