Ray-caster: don't bother clearing the screen

The ray-caster triangles cover the whole viewport, so they'll completely
overdraw the previous frame.

app-proto/inversive-display/src/main.rs

@@ -161,9 +161,7 @@ fn main() {
                 ctx.uniform1f(highlight_loc.as_ref(), highlight.get() as f32);
                 ctx.uniform1i(layer_threshold_loc.as_ref(), layer_threshold.get() as i32);
                 
-                // clear the screen and draw the scene
-                ctx.clear_color(0.0, 0.0, 0.0, 1.0);
-                ctx.clear(WebGl2RenderingContext::COLOR_BUFFER_BIT);
+                // draw the scene
                 ctx.draw_arrays(WebGl2RenderingContext::TRIANGLES, 0, VERTEX_CNT as i32);
             });
         });