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Tạo hình ảnh JPG, PNG,... trong Lập trình C với GD Librar

Mã nguồn
/* Bring in gd library functions */
#include "gd.h"

/* Bring in standard I/O so we can output the PNG to a file */
#include <stdio.h>

int main() {
  /* Declare the image */
  gdImagePtr im;
  /* Declare output files */
  FILE *pngout, *jpegout;
  /* Declare color indexes */
  int black;
  int white;

  /* Allocate the image: 64 pixels across by 64 pixels tall */
  im = gdImageCreate(64, 64);

  /* Allocate the color black (red, green and blue all minimum).
    Since this is the first color in a new image, it will
    be the background color. */
  black = gdImageColorAllocate(im, 0, 0, 0);

  /* Allocate the color white (red, green and blue all maximum). */
  white = gdImageColorAllocate(im, 255, 255, 255);

  /* Draw a line from the upper left to the lower right,
    using white color index. */
  gdImageLine(im, 0, 0, 63, 63, white);

  /* Open a file for writing. "wb" means "write binary", important
    under MSDOS, harmless under Unix. */
  pngout = fopen("test.png", "wb");

  /* Do the same for a JPEG-format file. */
  jpegout = fopen("test.jpg", "wb");

  /* Output the image to the disk file in PNG format. */
  gdImagePng(im, pngout);

  /* Output the same image in JPEG format, using the default
    JPEG quality setting. */
  gdImageJpeg(im, jpegout, -1);

  /* Close the files. */

  /* Destroy the image in memory. */

When executed, this program creates an image, allocates two colors (the first color allocated becomes the background color), draws a diagonal line (note that 0, 0 is the upper left corner), writes the image to PNG and JPEG files, and destroys the image.
The above example program should give you an idea of how the package works. gd provides many additional functions, which are listed in the following reference chapters, complete with code snippets demonstrating each.
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