feat: parameterize stroke color and thickness

shaders/triangle.frag.glsl

@@ -1,10 +1,10 @@
 #version 320 es
 precision mediump float;
 
-uniform vec4 uColor; // RGBA
-
+in vec4 vColor;
 out vec4 FragColor;
 
-void main() {
-    FragColor = uColor;
+void main()
+{
+    FragColor = vColor;
 }

shaders/triangle.vert.glsl

@@ -2,10 +2,14 @@
 precision mediump float;
 
 layout(location = 0) in vec2 aPos;
+layout (location = 1) in vec4 aColor;
 
 uniform mat4 uProjection;
 
+out vec4 vColor;
+
 void main()
 {
     gl_Position = uProjection * vec4(aPos, 0.0, 1.0);
-}
+    vColor = aColor;
+}