3 files changed, 65 insertions, 8 deletions
diff --git a/glow/src/shader/common/gradient.frag b/glow/src/shader/common/gradient.frag
new file mode 100644
index 00000000..42d0201f
--- /dev/null
+++ b/glow/src/shader/common/gradient.frag
@@ -0,0 +1,59 @@
+#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 vec4 gradient_direction;
+uniform uint color_stops_size;
+// GLSL does not support dynamically sized arrays without SSBOs so this is capped to 16 stops
+//stored as color(vec4) -> offset(vec4) sequentially;
+uniform vec4 color_stops[32];
+
+//TODO: rewrite without branching to make ALUs happy
+void main() {
+    vec2 start = gradient_direction.xy;
+    vec2 end = gradient_direction.zw;
+    vec2 gradient_vec = vec2(end - start);
+    vec2 current_vec = vec2(raw_position.xy - start);
+    vec2 unit = normalize(gradient_vec);
+    float coord_offset = dot(unit, current_vec) / length(gradient_vec);
+    //if a gradient has a start/end stop that is identical, the mesh will have a transparent fill
+    fragColor = vec4(0.0, 0.0, 0.0, 0.0);
+
+    float min_offset = color_stops[1].x;
+    float max_offset = color_stops[color_stops_size - 1u].x;
+
+    for (uint i = 0u; i < color_stops_size - 2u; i += 2u) {
+        float curr_offset = color_stops[i+1u].x;
+        float next_offset = color_stops[i+3u].x;
+
+        if (coord_offset <= min_offset) {
+            //current coordinate is before the first defined offset, set it to the start color
+            fragColor = color_stops[0];
+        }
+
+        if (curr_offset <= coord_offset && coord_offset <= next_offset) {
+            //current fragment is between the current offset processing & the next one, interpolate colors
+            fragColor = mix(color_stops[i], color_stops[i+2u], smoothstep(
+                curr_offset,
+                next_offset,
+                coord_offset
+            ));
+        }
+
+        if (coord_offset >= max_offset) {
+            //current coordinate is before the last defined offset, set it to the last color
+            fragColor = color_stops[color_stops_size - 2u];
+        }
+    }
+}
diff --git a/glow/src/shader/common/triangle.frag b/glow/src/shader/common/triangle.frag
index e8689f2e..ead40fe5 100644
--- a/glow/src/shader/common/triangle.frag
+++ b/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;
-}
-\ No newline at end of file
+    fragColor = color;
+}
diff --git a/glow/src/shader/common/triangle.vert b/glow/src/shader/common/triangle.vert
index d0494a5f..fe505997 100644
--- a/glow/src/shader/common/triangle.vert
+++ b/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;
-}
-\ No newline at end of file
+    raw_position = i_Position;
+}