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我目前正在关于在图像压缩中使用SDL的书。有一段代码可以在屏幕上显示图像，代码似乎读取图像，因为它会产生正确大小的窗口，但图像是黑色的。SDL生成黑色图像
我已经尝试了几个例子，所有的图像是黑色
我附上下面
#include <stdio.h>
#include <stdlib.h>
#include <SDL.h>
#include <string.h>
//A public class is the same as a 'struct'
class CImage {
public:
unsigned char red;
unsigned char green;
unsigned char blue;
};
void ppm_read_comments (FILE *fp)
{
int c;
while ((c = getc (fp)) == '#') {
while ( getc(fp) != '\n')
;
}
ungetc (c, fp);
}
class ppm_error
{
public:
ppm_error() {
printf("\nIncorrect PPM format!\n");
exit (1);
}
};
//change from (R, G, B) to (B, G, R)
void ppm2sdl (CImage *ibuf, int width, int height)
{
unsigned char temp;
for (int i = 0; i < height; ++i) {
int row_offset = i * width;
for (int j = 0; j < width; ++j){
int offset = row_offset + j;
temp = ibuf[offset].red;
ibuf[offset].red = ibuf[offset].blue;
ibuf[offset].blue = temp;
}
}
}
int main(int argc, char* args[])
{
int ppmh[20], c; //PPM header
int width, height; //image width and height
SDL_Surface *screen;
char filename[] = "C:/data/beach.ppm";
FILE *input = fopen (filename, "rb"); //PPM file for testing read
if (!input) {
printf("\nError opening input file %s!\n", filename);
return 1;
}
//read PPM input file
ppm_read_comments (input); //read comments
char temp[100];
fscanf (input, "%2s", temp);
temp[3] = 0;
if (strncmp (temp, "P6", 2))
throw ppm_error();
ppm_read_comments (input);
fscanf (input, "%d", &width);
ppm_read_comments (input);
fscanf (input, "%d", &height);
ppm_read_comments (input);
int colorlevels;
fscanf (input, "%d", &colorlevels);
printf("\n%s PPM file: ", temp);
printf(" \n\twidth=%d\theight=%d\tcolorlevles=%d\n", width,height,colorlevels+1);
ppm_read_comments (input);
while ((c = getc (input)) == '\n'); //get rid of extra line returns
ungetc (c ,input);
// May use CImage ibuf[width][height] if we do not use SDL_QUIT;
CImage *ibuf = (CImage *) malloc (width * height * 3);
fread (ibuf, 3, width * height, input); //read image data from file
fclose (input);
//initialize video system
if (SDL_Init(SDL_INIT_VIDEO) < 0) {
fprintf(stderr, "Unable to init SDL: %s\n", SDL_GetError());
exit(1);
}
//ensure SDL_Quit is called when the program exits
atexit(SDL_Quit); //if not use this, we need to
// do house cleaning manually when program ends
//set video mode of width x height with 24-bit pixels
screen = SDL_SetVideoMode(width, height, 24, SDL_SWSURFACE);
if (screen == NULL) {
fprintf(stderr, "Unable to set %dx%d video: %s\n", width, height, SDL_GetError());
exit(1);
}
//convert PPM format (R, G, B) to SDL format (B, G, R)
ppm2sdl (ibuf, width, height);
screen->pixels = ibuf; //point framebuffer to data buffer
// ibuf needs to be dynamically allocated if SDL_QUIT is used
printf("update rect\n" );
SDL_UpdateRect (screen, 0, 0, 0, 0); //blit data to screen
// SDL_Flip(screen);
// SDL_CreateRGBSurface(screen, 0, 0, 0, 0,0,0,0);
SDL_Delay (4000); //delay 4 seconds before exit
printf("Displaying PPM image %s successful!\n", filename);
//do NOT free(ibuf) if use SDL_QUIT which does the house cleaning
return 0;
}