C++ 使用libpng将OpenGL屏幕像素保存为PNG
我一直在使用SOIL将图像保存为BMP,但结果表明SOIL(或者更具体地说是stbi)保存了~5MB图像(约1366x768分辨率图像或更高),这是非常疯狂的 原始BMP保存代码(注意所有操作都在渲染功能中完成):C++ 使用libpng将OpenGL屏幕像素保存为PNG,c++,c,opengl,image-manipulation,libpng,C++,C,Opengl,Image Manipulation,Libpng,我一直在使用SOIL将图像保存为BMP,但结果表明SOIL(或者更具体地说是stbi)保存了~5MB图像(约1366x768分辨率图像或更高),这是非常疯狂的 原始BMP保存代码(注意所有操作都在渲染功能中完成): png_write_row然后在此处失败:(png_write_row的代码很长,因此如果您对此行之前发生的事情感到好奇,可以在png的源代码中查看pngwrite.c。) p.S:我在MinGW上使用了完全相同的代码,它100%正常工作,当我切换到MSVC时,它开始失败。我不确定G
png_write_row
然后在此处失败:(png_write_row的代码很长,因此如果您对此行之前发生的事情感到好奇,可以在png的源代码中查看pngwrite.c。)
p.S:我在MinGW上使用了完全相同的代码,它100%正常工作,当我切换到MSVC时,它开始失败。我不确定GCC是否在这里做了一些神奇的事情,或者这是我的代码的错误,因此为了学习,我想知道。下面一行:
rows[i]=(png_bytep)(像素+(h-i)*w*3)代码>
不幸地超过了内存块(像素
),因此下面的编辑修复了它:
rows[i]=(png_bytep)(像素+(h-i-1)*w*3)代码>
很琐碎,但不管怎样
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");
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;
}
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
}
}
}
/* Copy user's row into buffer, leaving room for filter byte. */
memcpy(png_ptr->row_buf + 1, row, row_info.rowbytes);