我将使用SOIL来保存BMP图片,但是SOIL(或具体点说是stbi)保存的图片大小约为5MB(大约是1366x768分辨率的图像或更高),这相当疯狂。
原始的BMP保存代码(注意:所有操作都在渲染函数中完成):
原始的BMP保存代码(注意:所有操作都在渲染函数中完成):
uint8_t *pixels = new uint8_t[w * h * 3];
// copy pixels from screen
glBindTexture(GL_TEXTURE_2D, screenTex);
glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, w, h);
glPixelStorei(GL_PACK_ALIGNMENT, 1);
glReadPixels(0, 0, w, h, GL_RGB, GL_UNSIGNED_BYTE, (GLvoid *)pixels);
// invert pixels (stolen from SOILs source code)
for (int j = 0; j * 2 < h; ++j) {
int x = j * w * 3;
int y = (h - 1 - j) * w * 3;
for (int i = w * 3; i > 0; --i) {
uint8_t tmp = pixels[x];
pixels[x] = pixels[y];
pixels[y] = tmp;
++x;
++y;
}
}
// save the image
int err = SOIL_save_image(fileName, SOIL_SAVE_TYPE_BMP, w, h, 3, pixels);
if (err)
printf("Done\n");
else
printf("Failed\n");
保存PNG格式的代码:
bool save_png_libpng(const char *filename, uint8_t *pixels, int w, int h)
{
png_structp png = png_create_write_struct(PNG_LIBPNG_VER_STRING, nullptr, nullptr, nullptr);
if (!png)
return false;
png_infop info = png_create_info_struct(png);
if (!info) {
png_destroy_write_struct(&png, &info);
return false;
}
FILE *fp = fopen(filename, "wb");
if (!fp) {
png_destroy_write_struct(&png, &info);
return false;
}
png_init_io(png, fp);
png_set_IHDR(png, info, w, h, 8 /* depth */, PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE,
PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
png_colorp palette = (png_colorp)png_malloc(png, PNG_MAX_PALETTE_LENGTH * sizeof(png_color));
if (!palette) {
fclose(fp);
png_destroy_write_struct(&png, &info);
return false;
}
png_set_PLTE(png, info, palette, PNG_MAX_PALETTE_LENGTH);
png_write_info(png, info);
png_set_packing(png);
png_bytepp rows = (png_bytepp)png_malloc(png, h * sizeof(png_bytep));
for (int i = 0; i < h; ++i)
rows[i] = (png_bytep)(pixels + (h - i) * w * 3);
png_write_image(png, rows);
png_write_end(png, info);
png_free(png, palette);
png_destroy_write_struct(&png, &info);
fclose(fp);
delete[] rows;
return true;
}
注意:我没有改变任何原始代码,只是将 SOIL_save_image
替换为 save_png
。
代码在以下行中失败:
png_write_image(png,rows)
在PNG源代码中,此函数在突出显示的行处失败:
void PNGAPI
png_write_image(png_structrp png_ptr, png_bytepp image)
{
png_uint_32 i; /* row index */
int pass, num_pass; /* pass variables */
png_bytepp rp; /* points to current row */
if (png_ptr == NULL)
return;
png_debug(1, "in png_write_image");
#ifdef PNG_WRITE_INTERLACING_SUPPORTED
/* Initialize interlace handling. If image is not interlaced,
* this will set pass to 1
*/
num_pass = png_set_interlace_handling(png_ptr);
#else
num_pass = 1;
#endif
/* Loop through passes */
for (pass = 0; pass < num_pass; pass++)
{
/* Loop through image */
for (i = 0, rp = image; i < png_ptr->height; i++, rp++)
{
png_write_row(png_ptr, *rp); // HERE
}
}
}
png_write_row
在这里失败了:(因为 png_write_row
的代码太长无法在此处张贴,所以如果您对该行之前发生的事情感到好奇,可以查看png源代码中的pngwrite.c文件。)
/* Copy user's row into buffer, leaving room for filter byte. */
memcpy(png_ptr->row_buf + 1, row, row_info.rowbytes);
P.S: 我曾在MinGW上使用完全相同的代码,它可以正常工作,但当我切换到MSVC时,它就失败了。我不确定是GCC在这里做了什么魔法,还是我的代码有问题,因此出于学习目的,我想知道原因。