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#include <stdio.h>
#include <gd.h>
#include <math.h>
void draw_exam_flag(gdImagePtr img);
void draw_white_sun(gdImagePtr img, int center_x, int center_y, int sun_radius, int white, int red, int blue);
int main() {
// width 3: height 2
int width = 1200;
int height = (int)(width*2.0 / 3.0);
gdImagePtr img = gdImageCreateTrueColor(width, height);
gdImageAlphaBlending(img, 0);
draw_exam_flag(img);
FILE *outputFile = fopen("./exam_flag.png", "wb");
if (outputFile == NULL) {
fprintf(stderr, "Error opening the output file.\n");
return 1;
}
gdImagePngEx(img, outputFile, 9);
fclose(outputFile);
gdImageDestroy(img);
return 0;
}
void draw_exam_flag(gdImagePtr img) {
int width = gdImageSX(img);
int height = gdImageSY(img);
int red, white, blue;
int center_x = (int)(width/4);
int center_y = (int)(height/4);
int sun_radius = (int)(width/8);
int lineColor = gdImageColorAllocate(img, 255, 255, 255);
// 畫一條線
int x1 = 429;
int y1 = 125;
int x2 = 170;
int y2 = 274;
int x3 = 279;
int y3 = 165;
int x4 = 170;
int y4 = 274;
int x5 = 279;
int y5 = 165;
int x6 = 429;
int y6 = 125;
// Colors for the flag
red = gdImageColorAllocate(img, 242, 0, 0); // Red color
white = gdImageColorAllocate(img, 255, 255, 255); // White stripes
blue = gdImageColorAllocate(img, 0, 41, 204); // Blue
// 繪製紅色矩形區域
gdImageFilledRectangle(img, 0, 0, width, height, red);
// 繪製藍色矩形區域
gdImageFilledRectangle(img, 0, 0, (int)(width/2.0), (int)(height/2.0), blue);
gdImageLine(img, x1, y1, x2, y2, lineColor);
gdImageLine(img, x3, y3, x4, y4, lineColor);
gdImageLine(img, x5, y5, x6, y6, lineColor);
return 0;
}
尋找交點
#include <stdio.h>
#include <gd.h>
#include <math.h>
void draw_roc_flag(gdImagePtr img);
void draw_white_sun(gdImagePtr img, int x, int y, int size, int color);
int main() {
// width 3: height 2
int width = 1200;
// 國旗長寬比為 3:2
int height = (int)(width*2.0 / 3.0);
gdImagePtr img = gdImageCreateTrueColor(width, height);
gdImageAlphaBlending(img, 0);
draw_roc_flag(img);
FILE *outputFile = fopen("roc_flag_in_gd.png", "wb");
if (outputFile == NULL) {
fprintf(stderr, "Error opening the output file.\n");
return 1;
}
gdImagePngEx(img, outputFile, 9);
fclose(outputFile);
gdImageDestroy(img);
return 0;
}
void draw_roc_flag(gdImagePtr img) {
int width = gdImageSX(img);
int height = gdImageSY(img);
int red, white, blue;
// 白日位於青天面積正中央, 因此中心點座標為長寬各 1/4 處
int center_x = (int)(width/4);
int center_y = (int)(height/4);
// gdImageFilledEllipse 需以長寬方向的 diameter 作圖
// 由於中央白日圓形的半徑為青天寬度的 1/8
// 因此中央白日圓形的直徑為青天寬度的 1/4, 也就是國旗寬度的 1/8
// 而且白日十二道光芒的外圍圓形其半徑也是國旗寬度的1/8
int sun_radius = (int)(width/8);
// 中央白日圓形的直徑等於十二道光芒外圍圓形的半徑
int white_circle_dia = sun_radius;
// 中央藍色圓形半徑為中央白日的 1又 2/15
int blue_circle_dia = white_circle_dia + white_circle_dia*2/15;
// 根據 https://www.moi.gov.tw/cp.aspx?n=10621 訂定國旗三種顏色值
red = gdImageColorAllocate(img, 255, 0, 0); // 紅色
white = gdImageColorAllocate(img, 255, 255, 255); // 白色
blue = gdImageColorAllocate(img, 0, 0, 149); // 藍色
// 根據畫布大小塗上紅色長方形區域
gdImageFilledRectangle(img, 0, 0, width, height, red);
// 青天面積為整面國旗的 1/4, 也是採用長方形塗色
gdImageFilledRectangle(img, 0, 0, (int)(width/2.0), (int)(height/2.0), blue);
{int x1 = 429;
int y1 = 125;
int x2 = 279;
int y2 = 165;
// 畫一條線連接兩個點
gdImageLine(img, x1, y1, x2, y2, white);
}
{int x1 = 170;
int y1 = 274;
int x2 = 279;
int y2 = 165;
// 畫一條線連接兩個點
gdImageLine(img, x1, y1, x2, y2, white);
}
{
int x1 = 170;
int y1 = 274;
int x2 = 429;
int y2 = 125;
// 畫一條線連接兩個點
gdImageLine(img, x1, y1, x2, y2, white);
}
// 利用一個藍色大圓與白色小圓畫出藍色環狀
gdImageFilledEllipse(img, center_x, center_y, blue_circle_dia, blue_circle_dia, blue);
gdImageFilledEllipse(img, center_x, center_y, white_circle_dia, white_circle_dia, white);
// 定義座標結構
typedef struct {
double x;
double y;
} Point;
// 計算圓與線的交點
void circleLineIntersection(double h, double k, double r, double x1, double y1, double x2, double y2) {
// 直線斜率
double m = (y2 - y1) / (x2 - x1);
// 直線方程式中的常數項
double b = y1 - m * x1;
// 圓與直線交點的計算
double A = 1 + pow(m, 2);
double B = 2 * (m * b - m * k - h);
double C = pow(k, 2) - pow(r, 2) + pow(h, 2) - 2 * b * k + pow(b, 2);
// 判斷交點個數
double discriminant = pow(B, 2) - 4 * A * C;
if (discriminant > 0) {
double x_intersect1 = (-B + sqrt(discriminant)) / (2 * A);
double y_intersect1 = m * x_intersect1 + b;
printf("交點: (%.2f, %.2f)\n", x_intersect1, y_intersect1);
double x_intersect2 = (-B - sqrt(discriminant)) / (2 * A);
double y_intersect2 = m * x_intersect2 + b;
printf("交點: (%.2f, %.2f)\n", x_intersect2, y_intersect2);
} else if (discriminant == 0) {
double x_intersect = -B / (2 * A);
double y_intersect = m * x_intersect + b;
printf("交點: (%.2f, %.2f)\n", x_intersect, y_intersect);
} else {
printf("No points.\n");
}
}
// 圓的參數
double circle_x = (int)(width/4); // 圓心 x 座標
double circle_y = (int)(height/4); // 圓心 y 座標
double radius = white_circle_dia + white_circle_dia*2/15; // 圓半徑
// 兩點座標
double x3 = 170;
double y3 = 274;
double x4 = 279;
double y4 = 165;
circleLineIntersection(circle_x, circle_y, radius, x4, y4, x3, y3);
double x5 = 279;
double y5 = 165;
double x6 = 429;
double y6 = 125;
circleLineIntersection(circle_x, circle_y, radius, x6, y6, x5, y5);
}
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