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美國國旗

程式如下
#include <stdio.h>
#include <gd.h>
#include <math.h>

void draw_usa_flag(gdImagePtr img);
void draw_star(gdImagePtr img, int x, int y, int size, int color, double rotation_angle);

int main() {
int width = 800;
int height = (int)(width / 1.9);

gdImagePtr img = gdImageCreateTrueColor(width, height);
gdImageAlphaBlending(img, 0);

draw_usa_flag(img);

FILE *outputFile = fopen("./../images/usa_flag.png", "wb");
if (outputFile == NULL) {
fprintf(stderr, "打开输出文件时出错。\n");
return 1;
}

gdImagePngEx(img, outputFile, 9);
fclose(outputFile);
gdImageDestroy(img);

return 0;
}

void draw_usa_flag(gdImagePtr img) {
int width = gdImageSX(img);
int height = gdImageSY(img);
int red, white, blue;
// 国旗颜色
red = gdImageColorAllocate(img, 178, 34, 52); // 红色条纹
white = gdImageColorAllocate(img, 255, 255, 255); // 白色条纹
blue = gdImageColorAllocate(img, 60, 59, 110); // 蓝色矩形

int stripe_height = height / 13;
int stripe_width = width;
int star_size = (int)(0.0308 * height); // 星星大小

for (int y = 0; y < height; y += stripe_height) {
if (y / stripe_height % 2 == 0) {
gdImageFilledRectangle(img, 0, y, stripe_width, y + stripe_height, red);
} else {
gdImageFilledRectangle(img, 0, y, stripe_width, y + stripe_height, white);
}
}

gdImageFilledRectangle(img, 0, 0, width * 2 / 5, stripe_height * 7, blue);

int star_spacing_x = (int)(0.129 * height); // 横向星星之间的间距
int star_spacing_y = (int)(0.054 * height); // 纵向星星之间的间距
int star_start_x = (int)(0.125 * height); // 星星的起始X位置
int star_start_y = (int)(0.0485 * height); // 星星的起始Y位置

for (int row = 0; row < 9; row++) {
int starsPerRow = (row % 2 == 0) ? 6 : 5;

// 计算2、4、6和8排星星的偏移量
int offset_x = (row % 2 == 0) ? star_spacing_x / -2 : 0;

for (int star = 0; star < starsPerRow; star++) {
int x = star_start_x + star * star_spacing_x + offset_x;

// 旋转角度（以弧度为单位）
double rotation_angle = M_PI / 5; // 忘記多少度的旋转

int y = star_start_y + row * star_spacing_y;
draw_star(img, x, y, star_size, white, rotation_angle);
}
}
}

void draw_star(gdImagePtr img, int x, int y, int size, int color, double rotation_angle) {
gdPoint points[10];

for (int i = 0; i < 10; i++) {
double angle = M_PI / 2 + i * 2 * M_PI / 10 + rotation_angle;
int radius = (i % 2 == 0) ? size : size / 2;
points[i].x = x + radius * cos(angle);
points[i].y = y + radius * sin(angle);
}

// 用指定的颜色填充星星
gdImageFilledPolygon(img, points, 10, color);
}
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