C语言使用gd库函数详细记录

1.绘图函数

（1）绘制一个像素点的函数

　　void gdImageSetPixel(gdImagePtr im, int x, int y, int color)

　　参数列表

　　第一参数：gdImagePtr类型，为对象

　　第二参数：画图的横坐标

　　第三参数：画图纵坐标

　　第四参数：要绘制的颜色

（2）在两个端点之间画一条直线

　  void gdImageLine(gdImagePtr im, int x1, int y1, int x2, int y2, int color)

　　参数列表依次是：对象，两个端点的坐标，颜色

（3）用于绘制一个多边形的函数，至少三个

void gdImagePolygon(gdImagePtr im, gdPointPtr points, int pointsTotal, int color)

具体事例

#include<stdio.h>
#include <gdfontl.h>
#include <gd.h>
#include <string.h>

int main(int argc,char **argv)
{
gdImagePtr im;
FILE*pngout;
int black;
int white;
/* Points of polygon */
gdPoint points[3];
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and
blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Draw a triangle. */
points[0].x = 50;
points[0].y = 0;
points[1].x = 99;
points[1].y = 99;
points[2].x = 0;
points[2].y = 99;
gdImagePolygon(im, points, 3, white);
/* ... Do something with the image, such as
saving it to a file... */
/* Destroy it */
pngout = fopen("test1.png","wb");
gdImagePng(im, pngout);
fclose(pngout);
gdImageDestroy(im);

return 0;

}

 

（4） 剪切区域的函数

void gdImageSetClip(gdImagePtr im, int x1, int y1, int x2, int y2) 

参数分别为起始坐标和终止坐标，建立了剪切长方形。一旦gdImageSetClip被调用,未来所有的绘图操作仍将在指定剪裁区域,直到一个新的gdImageSetClip调用。

示例

#include<stdio.h>
#include <gdfontl.h>
#include <gd.h>
#include <string.h>

int main(int argc,char **argv)
{
gdImagePtr im;
FILE*pngout;
int black;
int white;
im = gdImageCreate(100, 100);
/* Background color (first allocated) */
black = gdImageColorAllocate(im, 0, 0, 0);
/* Allocate the color white (red, green and blue all maximum). */
white = gdImageColorAllocate(im, 255, 255, 255);
/* Set the clipping rectangle. */
gdImageSetClip(im, 25, 25, 75, 75);
/* Draw a line from the upper left corner to the lower right corner.
Only the part within the clipping rectangle will appear. */
gdImageLine(im, 0, 0, 99, 99, white);
/* ... Do something with the image, such as
saving it to a file ... */
/* Destroy it */
pngout = fopen("test1.png","wb");
gdImagePng(im, pngout);
fclose(pngout);
gdImageDestroy(im);

return 0;
}

（5）void gdImageGetClip(gdImagePtr im, int *x1P, int *y1P, int *x2P, int *y2P)

获取剪切矩形的边界

gdImagePtr im = gdImageCreateTrueColor(100, 100);
int x1, y1, x2, y2;
gdImageSetClip(im, 25, 25, 75, 75);
gdImageGetClip(im, &x1, &y1, &x2, &y2);
printf("%d %d %d %d\n", x1, y1, x2, y2);

The above code would print:

25 25 75 75