add antialiased line shader

1 files changed, 15 insertions, 0 deletions

diff --git a/src/shader/outline.vertex.glsl b/src/shader/outline.vertex.glsl
new file mode 100644
index 0000000000..c3d608fd70
--- /dev/null
+++ b/src/shader/outline.vertex.glsl
@@ -0,0 +1,15 @@
+attribute vec2 a_pos;
+uniform mat4 u_matrix;
+uniform vec2 u_world;
+
+varying vec2 v_pos;
+
+void main() {
+    // If the x coordinate is the maximum integer, we move the z coordinates out
+    // of the view plane so that the triangle gets clipped. This makes it easier
+    // for us to create degenerate triangle strips.
+    float z = step(32767.0, a_pos.x) * 2.0;
+    gl_Position = u_matrix * vec4(a_pos, z, 1);
+
+    v_pos = (gl_Position.xy + 1.0) / 2.0 * u_world;
+}