Mercurial > repos > blastem
view shaders/ntsc.f.glsl @ 2354:a773b8f09292
Remove old refresh hack that is causing VDPFifoTesting to have a failed test
author | Michael Pavone <pavone@retrodev.com> |
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date | Thu, 19 Oct 2023 23:27:57 -0700 |
parents | 49bd818ec9d8 |
children | f1574b22d5d9 |
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//****************************************************************************** // NTSC composite simulator for BlastEm // Shader by Sik, based on BlastEm's default shader // // Now with gamma correction (NTSC = 2.5 gamma, sRGB = 2.2 gamma) // // It works by converting from RGB to YIQ and then encoding it into NTSC, then // trying to decode it back. The lossy nature of the encoding process results in // the rainbow effect. It also accounts for the differences between H40 and H32 // mode as it computes the exact colorburst cycle length. // // This shader tries to work around the inability to keep track of previous // pixels by sampling seven points (in 0.25 colorburst cycle intervals), that // seems to be enough to give decent filtering (four samples are used for // low-pass filtering, but we need seven because decoding chroma also requires // four samples so we're filtering over overlapping samples... just see the // comments in the I/Q code to understand). //****************************************************************************** uniform mediump float width; uniform sampler2D textures[2]; uniform mediump vec2 texsize; varying mediump vec2 texcoord; // Converts from RGB to YIQ mediump vec3 rgba2yiq(vec4 rgba) { return vec3( rgba[0] * 0.3 + rgba[1] * 0.59 + rgba[2] * 0.11, rgba[0] * 0.599 + rgba[1] * -0.2773 + rgba[2] * -0.3217, rgba[0] * 0.213 + rgba[1] * -0.5251 + rgba[2] * 0.3121 ); } // Encodes YIQ into composite mediump float yiq2raw(vec3 yiq, float phase) { return yiq[0] + yiq[1] * sin(phase) + yiq[2] * cos(phase); } // Converts from YIQ to RGB mediump vec4 yiq2rgba(vec3 yiq) { return vec4( yiq[0] + yiq[1] * 0.9469 + yiq[2] * 0.6236, yiq[0] - yiq[1] * 0.2748 - yiq[2] * 0.6357, yiq[0] - yiq[1] * 1.1 + yiq[2] * 1.7, 1.0 ); } void main() { // Use first pair of lines for hard line edges // Use second pair of lines for soft line edges mediump float modifiedY0 = (floor(texcoord.y * texsize.y + 0.25) + 0.5) / texsize.y; mediump float modifiedY1 = (floor(texcoord.y * texsize.y - 0.25) + 0.5) / texsize.y; //mediump float modifiedY0 = (texcoord.y * texsize.y + 0.75) / texsize.y; //mediump float modifiedY1 = (texcoord.y * texsize.y + 0.25) / texsize.y; // Used by the mixing when fetching texels, related to the way BlastEm // handles interlaced mode (nothing to do with composite) mediump float factorY = (sin(texcoord.y * texsize.y * 6.283185307) + 1.0) * 0.5; // Horizontal distance of half a colorburst cycle mediump float factorX = (1.0 / texsize.x) / 170.667 * 0.5 * (width - 27.0); // sRGB has a gamma of 2.2 while NTSC has a gamma of 2.5 // Use this value to do gamma correction of every RGB value mediump float gamma = 2.5 / 2.2; // Where we store the sampled pixels. // [0] = current pixel // [1] = 1/4 colorburst cycles earlier // [2] = 2/4 colorburst cycles earlier // [3] = 3/4 colorburst cycles earlier // [4] = 1 colorburst cycle earlier // [5] = 1 1/4 colorburst cycles earlier // [6] = 1 2/4 colorburst cycles earlier mediump float phase[7]; // Colorburst phase (in radians) mediump float raw[7]; // Raw encoded composite signal // Sample all the pixels we're going to use mediump float x = texcoord.x; for (int n = 0; n < 7; n++, x -= factorX * 0.5) { // Compute colorburst phase at this point phase[n] = x / factorX * 3.1415926; // Decode RGB into YIQ and then into composite // Reading two textures is a BlastEm thing :P (the two fields in // interlaced mode, that's taken as-is from the stock shaders) raw[n] = yiq2raw(mix( rgba2yiq(texture2D(textures[1], vec2(x, modifiedY1))), rgba2yiq(texture2D(textures[0], vec2(x, modifiedY0))), factorY ), phase[n]); } // Decode Y by averaging over the the whole sampled cycle (effectively // filtering anything above the colorburst frequency) mediump float y_mix = (raw[0] + raw[1] + raw[2] + raw[3]) * 0.25; // Decode I and Q (see page below to understand what's going on) // https://codeandlife.com/2012/10/09/composite-video-decoding-theory-and-practice/ // // Retrieving I and Q out of the raw signal is done like this // (use sin for I and cos for Q): // // 0.5 * raw[0] * sin(phase[0]) + 0.5 * raw[1] * sin(phase[1]) + // 0.5 * raw[2] * sin(phase[2]) + 0.5 * raw[3] * sin(phase[3]) // // i.e. multiply each of the sampled quarter cycles against the reference // wave and average them (actually double that because for some reason // that's needed to get the correct scale, hence 0.5 instead of 0.25) // // That turns out to be blocky tho, so we opt to filter down the chroma... // which requires doing the above *four* times if we do it the same way as // we did for luminance (note that 0.125 = 1/4 of 0.5): // // 0.125 * raw[0] * sin(phase[0]) + 0.125 * raw[1] * sin(phase[1]) + // 0.125 * raw[2] * sin(phase[2]) + 0.125 * raw[3] * sin(phase[3]) + // 0.125 * raw[1] * sin(phase[1]) + 0.125 * raw[2] * sin(phase[2]) + // 0.125 * raw[3] * sin(phase[3]) + 0.125 * raw[4] * sin(phase[4]) + // 0.125 * raw[2] * sin(phase[2]) + 0.125 * raw[3] * sin(phase[3]) + // 0.125 * raw[4] * sin(phase[4]) + 0.125 * raw[5] * sin(phase[5]) + // 0.125 * raw[3] * sin(phase[3]) + 0.125 * raw[4] * sin(phase[4]) + // 0.125 * raw[5] * sin(phase[5]) + 0.125 * raw[6] * sin(phase[6]) // // There are a lot of repeated values there that could be merged into one, // what you see below is the resulting simplification. mediump float i_mix = 0.125 * raw[0] * sin(phase[0]) + 0.25 * raw[1] * sin(phase[1]) + 0.375 * raw[2] * sin(phase[2]) + 0.5 * raw[3] * sin(phase[3]) + 0.375 * raw[4] * sin(phase[4]) + 0.25 * raw[5] * sin(phase[5]) + 0.125 * raw[6] * sin(phase[6]); mediump float q_mix = 0.125 * raw[0] * cos(phase[0]) + 0.25 * raw[1] * cos(phase[1]) + 0.375 * raw[2] * cos(phase[2]) + 0.5 * raw[3] * cos(phase[3]) + 0.375 * raw[4] * cos(phase[4]) + 0.25 * raw[5] * cos(phase[5]) + 0.125 * raw[6] * cos(phase[6]); // Convert YIQ back to RGB and output it gl_FragColor = pow(yiq2rgba(vec3(y_mix, i_mix, q_mix)), vec4(gamma, gamma, gamma, 1.0)); // If you're curious to see what the raw composite signal looks like, // comment out the above and uncomment the line below instead //gl_FragColor = vec4(raw[0], raw[0], raw[0], 1.0); }