Create a shader program that draws a rectangular frame border around the screen. The border width is 50 pixels. Use uv coordinates as the frame border color.
Use the step function to draw each border separately. Next, combine the borders together to create a frame. To do this, you only need to compute the union of the test results.
The shader should avoid using branching or conditional statements in its code, and instead rely on the step and max functions to determine the color of each pixel.