implement DrawLine with shader

data/shaders/drawline.frag

@@ -0,0 +1,20 @@
+#version 330
+
+uniform ivec2   uScreenSize;
+uniform ivec4   uClip;
+uniform vec4    uColour;
+
+in vec2 fPosition;
+
+layout (location = 0) out vec4 oColour;
+
+void main()
+{
+    if (fPosition.x < uClip.x || fPosition.x > uClip.z ||
+        fPosition.y < uClip.y || fPosition.y > uClip.w)
+    {
+        discard;
+    }
+
+    oColour = uColour;
+}

data/shaders/drawline.vert

@@ -0,0 +1,30 @@
+#version 330
+
+uniform ivec2 uScreenSize;
+uniform ivec4 uBounds;
+
+in int vIndex;
+
+out vec2 fPosition;
+
+void main()
+{
+    vec2 pos;
+    if (vIndex == 0)
+    {
+        pos = uBounds.xy;
+    }
+    else
+    {
+        pos = uBounds.zw;
+    }
+
+    fPosition = pos;
+
+    // Transform screen coordinates to viewport
+    pos.x = (pos.x * (2.0 / uScreenSize.x)) - 1.0;
+    pos.y = (pos.y * (2.0 / uScreenSize.y)) - 1.0;
+    pos.y *= -1;
+
+    gl_Position = vec4(pos, 0.0, 1.0);
+}