Fix clear() on framebuffers on Intel macs

src/webgl/p5.RendererGL.js

@@ -1312,6 +1312,21 @@ p5.RendererGL = class RendererGL extends p5.Renderer {
     const _b = args[2] || 0;
     const _a = args[3] || 0;
 
+    const activeFramebuffer = this.activeFramebuffer();
+    if (
+      activeFramebuffer &&
+      activeFramebuffer.format === constants.UNSIGNED_BYTE &&
+      !activeFramebuffer.antialias &&
+      _a === 0
+    ) {
+      // Drivers on Intel Macs check for 0,0,0,0 exactly when drawing to a
+      // framebuffer and ignore the command if it's the only drawing command to
+      // the framebuffer. To work around it, we can set the alpha to a value so
+      // low that it still rounds down to 0, but that circumvents the buggy
+      // check in the driver.
+      a = 1e-10;
+    }
+
     this.GL.clearColor(_r * _a, _g * _a, _b * _a, _a);
     this.GL.clearDepth(1);
     this.GL.clear(this.GL.COLOR_BUFFER_BIT | this.GL.DEPTH_BUFFER_BIT);