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July 27, 2024 09:06
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Draw a Sierpinski triangle using Chaos game
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| #include <gd.h> | |
| // C doesn't allow variable length arrays (even using a constant) | |
| #define N_CORNERS 3 | |
| typedef struct { | |
| int x; | |
| int y; | |
| } Point; | |
| /** | |
| * Draw a Sierpinski triangle using Chaos game | |
| * - Js implementation: https://www.youtube.com/watch?v=7gNzMtYo9n4 | |
| * - Description: https://mathigon.org/course/fractals/sierpinski | |
| * - GD documentation: https://libgd.github.io/manuals/2.1.1/files/preamble-txt.html | |
| * | |
| * How to build & run: | |
| * $ gcc -lgd sierpinski.c -o sierpinski | |
| * $ ./sierpinski image.png 500 500 | |
| */ | |
| int main(int argc, char** argv) { | |
| if (argc != 4) { | |
| printf("USAGE: %s IMAGE WIDTH HEIGHT\n", argv[0]); | |
| return 1; | |
| } | |
| const char* filename = argv[1]; | |
| FILE* file = fopen(filename, "wb"); | |
| // rgb image | |
| const int WIDTH = atoi(argv[2]); | |
| const int HEIGHT = atoi(argv[3]); | |
| gdImagePtr image = gdImageCreateTrueColor(WIDTH, HEIGHT); | |
| // colors | |
| const int RED = gdTrueColor(0xff, 0, 0); | |
| const int GREEN = gdTrueColor(0, 0xff, 0); | |
| const int BLUE = gdTrueColor(0, 0, 0xff); | |
| int colors[N_CORNERS] = { RED, GREEN, BLUE }; | |
| // three triangle corners | |
| Point corner0 = { WIDTH / 2, 0 }; | |
| Point corner1 = { 0, HEIGHT }; | |
| Point corner2 = { WIDTH - 1, HEIGHT - 1 }; | |
| Point corners[N_CORNERS] = { corner0, corner1, corner2 }; | |
| for (size_t i_corner = 0; i_corner < N_CORNERS; ++i_corner) { | |
| gdImageSetPixel(image, corners[i_corner].x, corners[i_corner].y, colors[i_corner]); | |
| } | |
| /* chaos game */ | |
| const int N_ITERS = 100000; | |
| Point point = { rand() % WIDTH, rand() % HEIGHT }; | |
| for (size_t i_iter = 0; i_iter < N_ITERS; ++i_iter) { | |
| int i_corner = rand() % N_CORNERS; | |
| Point corner = corners[i_corner]; | |
| Point avg = { (point.x + corner.x) / 2, (point.y + corner.y) / 2 }; | |
| point = avg; | |
| gdImageSetPixel(image, point.x, point.y, colors[i_corner]); | |
| } | |
| gdImagePng(image, file); | |
| // free assets | |
| fclose(file); | |
| gdImageDestroy(image); | |
| return 0; | |
| } |
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