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copied!<p>Many of these points have been covered by others who have posted answers, but the overarching theme here is that your rendering does a lot of work that will be thrown away:</p> <ol> <li><p><strong>The shader itself does some potentially redundant work.</strong> The length of a vector is likely to be calculated as <code>sqrt(dot(vector, vector))</code>. You don’t need the sqrt to reject fragments outside of the circle, and you’re squaring the length to calculate the depth, anyway. Additionally, have you looked at whether or not explicit quantization of the depth values is actually necessary, or can you get away with just using the hardware’s conversion from floating-point to integer for the framebuffer (potentially with an additional bias to make sure your quasi-depth tests come out right later)?</p></li> <li><p><strong>Many fragments are trivially outside the circle.</strong> Only π/4 of the area of the quads you’re drawing produce useful depth values. At this point, I imagine your app is heavily skewed towards fragment processing, so you may want to consider increasing the number of vertices you draw in exchange for a reduction in the area that you have to shade. Since you’re drawing spheres through an orthographic projection, any circumscribing regular polygon will do, although you may need a little extra size depending on zoom level to make sure you rasterize enough pixels.</p></li> <li><p><strong>Many fragments are trivially occluded by other fragments.</strong> As others have pointed out, you’re not using hardware depth test, and therefore not taking full advantage of a TBDR’s ability to kill shading work early. If you’ve already implemented something for 2), all you need to do is draw an inscribed regular polygon at the maximum depth that you can generate (a plane through the middle of the sphere), and draw your real polygon at the minimum depth (the front of the sphere). Both Tommy’s and rotoglup’s posts already contain the state vector specifics.</p></li> </ol> <p>Note that 2) and 3) apply to your raytracing shaders as well.</p>

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