Adds linear gradient support to 2D meshes in the canvas widget.

glow/src/shader/common/gradient.frag

@@ -0,0 +1,48 @@
+// GLSL does not support dynamically sized arrays without SSBOs
+#define MAX_STOPS 64
+
+#ifdef GL_ES
+#ifdef GL_FRAGMENT_PRECISION_HIGH
+precision highp float;
+#else
+precision mediump float;
+#endif
+#endif
+
+#ifdef HIGHER_THAN_300
+layout (location = 0) out vec4 fragColor;
+#define gl_FragColor fragColor
+#endif
+
+in vec2 raw_position;
+
+uniform vec2 gradient_start;
+uniform vec2 gradient_end;
+
+uniform uint color_stops_size;
+uniform float color_stop_offsets[MAX_STOPS];
+uniform vec4 color_stop_colors[MAX_STOPS];
+
+void main() {
+    vec2 gradient_vec = vec2(gradient_end - gradient_start);
+    vec2 current_vec = vec2(raw_position.xy - gradient_start);
+    vec2 unit = normalize(gradient_vec);
+    float coord_offset = dot(unit, current_vec) / length(gradient_vec);
+
+    for (uint i = 0; i < color_stops_size - 1; i++) {
+        float stop_offset = color_stop_offsets[i];
+        float next_stop_offset = color_stop_offsets[i + 1];
+
+        if (stop_offset <= coord_offset && coord_offset <= next_stop_offset) {
+            fragColor = mix(color_stop_colors[i], color_stop_colors[i+1], smoothstep(
+                stop_offset,
+                next_stop_offset,
+                coord_offset
+            ));
+        } else if (coord_offset < color_stop_offsets[0]) {
+            fragColor = color_stop_colors[0];
+        } else if (coord_offset > color_stop_offsets[color_stops_size - 1]) {
+            fragColor = color_stop_colors[color_stops_size - 1];
+        }
+    }
+}

glow/src/shader/common/triangle.frag

@@ -11,8 +11,8 @@ out vec4 fragColor;
 #define gl_FragColor fragColor
 #endif
 
-in vec4 v_Color;
+uniform vec4 color;
 
 void main() {
-    gl_FragColor = v_Color;
+    fragColor = color;
 }

glow/src/shader/common/triangle.vert

@@ -1,11 +1,9 @@
 uniform mat4 u_Transform;
 
 in vec2 i_Position;
-in vec4 i_Color;
-
-out vec4 v_Color;
+out vec2 raw_position;
 
 void main() {
     gl_Position = u_Transform * vec4(i_Position, 0.0, 1.0);
-    v_Color = i_Color;
+    raw_position = i_Position;
 }