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@fpsunflower
Last active December 9, 2021 14:42
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Tiny OpenEXR output
// c++ -o nanoexr nanoexr.cpp && ./nanoexr /tmp/foo.exr
#include <cstdio>
// writes a tiled OpenEXR file from a float RGB buffer
struct Exr {
FILE* f; enum{TS=64}; ~Exr() { fclose(f); }
void B(unsigned char i) { fputc(i,f); }
void I(unsigned int i) { fwrite(&i,1,4,f); }
void L(unsigned long long i) { fwrite(&i,1,8,f); }
void F(float x) { fwrite(&x,1,4,f); }
void S(const char* str) { fputs(str,f);B(0); }
void C(const char* name) { S(name);L(2);I(1);I(1); }
Exr(const char* fn, int w, int h, const float* c) : f(fopen(fn, "w")) {
I(20000630);I(514); // magic/version/tiled
S("channels");S("chlist");I(55);C("B");C("G");C("R");B(0);
S("compression");S("compression");I(1);B(0);
S( "dataWindow");S("box2i");I(16);I(0);I(0);I(w-1);I(h-1);
S("displayWindow");S("box2i");I(16);I(0);I(0);I(w-1);I(h-1);
S("lineOrder");S("lineOrder");I(1);B(2);
S("pixelAspectRatio");S("float");I(4);F(1.0f);
S("screenWindowCenter");S("v2f");I(8);F(0.0f);F(0.0f);
S("screenWindowWidth");S("float");I(4);F(1.0f);
S("tiles");S("tiledesc");I(9);I(TS);I(TS);B(0);B(0);
int tx = (w + TS - 1) / TS, ty = (h + TS - 1) / TS;
long off = ftell(f) + tx * ty * 8; float out[TS * 3];
for (int k = 2; k--;) for (int y = 0; y < h; y += TS)
for (int x = 0; x < w; x += TS) {
int tw = w-x > TS ? TS : w-x;
int th = h-y > TS ? TS : h-y, sz=tw*th*12;
if (k) { L(off); off += 20 + sz; continue; }
I(x / TS);I(y / TS);I(0);I(0);I(sz);
for (int ty = 0; ty < th; ty++) {
const float* in = c + 3 * (x+w*(y+ty));
for (int tx = 0; tx < tw; tx++)
out[ tx] = in[3*tx+2],
out[ tw+tx] = in[3*tx+1],
out[tw+tw+tx] = in[3*tx+0];
fwrite(out, 12, tw, f);
}
}
}
};
// example usage
int main(int argc, const char** argv) {
int w = 640, h = 480;
float* image = new float[3 * w * h];
for (int y = 0, idx = 0; y < h; y++)
for (int x = 0; x < w; x++, idx += 3)
image[idx + 0] = float(x) / w,
image[idx + 1] = float(y) / h,
image[idx + 2] = 0;
Exr(argc < 2 ? "/tmp/test.exr" : argv[1], w, h, image);
delete [] image;
}
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