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POanti-aliased pixel rendering
 

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    <p>I'm trying to implement anti-aliased pixel rendering. My basic idea is to render 4 pixels instead of 1, and give each "real" pixel a weight based on its distance to the "virtual" pixel:</p> <pre><code>void put_aa_pixel(double x, double y) { int x0 = int(x); int x1 = x0 + 1; int y0 = int(y); int y1 = y0 + 1; double weight_x1 = x - x0; double weight_x0 = 1 - weight_x1; double weight_y1 = y - y0; double weight_y0 = 1 - weight_x1; put_pixel(x0, y0, int((weight_x0 * weight_y0) * 255)); put_pixel(x1, y0, int((weight_x1 * weight_y0) * 255)); put_pixel(x0, y1, int((weight_x0 * weight_y1) * 255)); put_pixel(x1, y1, int((weight_x1 * weight_y1) * 255)); } </code></pre> <p>Multiplying the x and y weights gives me the overlapping area of the virtual pixel inside each real pixel. I naively assumed this would give me a perfect anti-aliasing effect, but the moving pixels inside my test program just display an aweful flicker. It looks much worse then simple pixels without any anti-aliasing.</p> <p>However, when I switch from multiplication to addition, it looks much better:</p> <pre><code> put_pixel(x0, y0, int((weight_x0 + weight_y0) * 127.5)); put_pixel(x1, y0, int((weight_x1 + weight_y0) * 127.5)); put_pixel(x0, y1, int((weight_x0 + weight_y1) * 127.5)); put_pixel(x1, y1, int((weight_x1 + weight_y1) * 127.5)); </code></pre> <p>Adding the weights doesn't seem to have any geometric significance. So why does this work better? What's wrong with the first version? And is there an even better approach?</p>
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    1. COJust wondering, why not use a graphics library like OpenGL that does all this for you?
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      1. USMatt Phillips
    2. CO@Matt: I want to know how stuff works ;)
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    3. COIntuitively: your x and y weights express distance along axis from virtual to real pixel. So, the actual distance is sqrt(w_x^2 + w_y^2). Explains why sum works better - it's way closer to this form than multiplication.
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