我正在使用 stb 库为 OpenGL 动态加载纹理。我正在尝试使用 stb_image_write.h 中的函数。我找不到有关如何正确使用函数 stbi_write_png_to_mem
的任何文档,我的代码如下所示
#ifndef STB_IMAGE_WRITE_IMPLEMENTATION
#define STB_IMAGE_WRITE_IMPLEMENTATION
#include <stb/stb_image_write.h>
int main( )
{
// data is filled in later in program
int size , width , height ;
unsigned char* data = ( unsigned char* ) malloc( width * height ) ;
...
...
...
// this is where the issue lies
stbi_write_png_to_mem( ) ;
}
我查看了 github 并查看了源代码本身。我在谷歌上找不到任何东西。我不确定这个函数的输入是什么,因为不清楚什么是什么意思。函数的源代码是
STBIWDEF unsigned char *stbi_write_png_to_mem(const unsigned char *pixels, int stride_bytes, int x, int y, int n, int *out_len)
{
int force_filter = stbi_write_force_png_filter;
int ctype[5] = { -1, 0, 4, 2, 6 };
unsigned char sig[8] = { 137,80,78,71,13,10,26,10 };
unsigned char *out,*o, *filt, *zlib;
signed char *line_buffer;
int j,zlen;
if (stride_bytes == 0)
stride_bytes = x * n;
if (force_filter >= 5) {
force_filter = -1;
}
filt = (unsigned char *) STBIW_MALLOC((x*n+1) * y); if (!filt) return 0;
line_buffer = (signed char *) STBIW_MALLOC(x * n); if (!line_buffer) { STBIW_FREE(filt); return 0; }
for (j=0; j < y; ++j) {
int filter_type;
if (force_filter > -1) {
filter_type = force_filter;
stbiw__encode_png_line((unsigned char*)(pixels), stride_bytes, x, y, j, n, force_filter, line_buffer);
} else { // Estimate the best filter by running through all of them:
int best_filter = 0, best_filter_val = 0x7fffffff, est, i;
for (filter_type = 0; filter_type < 5; filter_type++) {
stbiw__encode_png_line((unsigned char*)(pixels), stride_bytes, x, y, j, n, filter_type, line_buffer);
// Estimate the entropy of the line using this filter; the less, the better.
est = 0;
for (i = 0; i < x*n; ++i) {
est += abs((signed char) line_buffer[i]);
}
if (est < best_filter_val) {
best_filter_val = est;
best_filter = filter_type;
}
}
if (filter_type != best_filter) { // If the last iteration already got us the best filter, don't redo it
stbiw__encode_png_line((unsigned char*)(pixels), stride_bytes, x, y, j, n, best_filter, line_buffer);
filter_type = best_filter;
}
}
// when we get here, filter_type contains the filter type, and line_buffer contains the data
filt[j*(x*n+1)] = (unsigned char) filter_type;
STBIW_MEMMOVE(filt+j*(x*n+1)+1, line_buffer, x*n);
}
STBIW_FREE(line_buffer);
zlib = stbi_zlib_compress(filt, y*( x*n+1), &zlen, stbi_write_png_compression_level);
STBIW_FREE(filt);
if (!zlib) return 0;
// each tag requires 12 bytes of overhead
out = (unsigned char *) STBIW_MALLOC(8 + 12+13 + 12+zlen + 12);
if (!out) return 0;
*out_len = 8 + 12+13 + 12+zlen + 12;
o=out;
STBIW_MEMMOVE(o,sig,8); o+= 8;
stbiw__wp32(o, 13); // header length
stbiw__wptag(o, "IHDR");
stbiw__wp32(o, x);
stbiw__wp32(o, y);
*o++ = 8;
*o++ = STBIW_UCHAR(ctype[n]);
*o++ = 0;
*o++ = 0;
*o++ = 0;
stbiw__wpcrc(&o,13);
stbiw__wp32(o, zlen);
stbiw__wptag(o, "IDAT");
STBIW_MEMMOVE(o, zlib, zlen);
o += zlen;
STBIW_FREE(zlib);
stbiw__wpcrc(&o, zlen);
stbiw__wp32(o,0);
stbiw__wptag(o, "IEND");
stbiw__wpcrc(&o,0);
STBIW_ASSERT(o == out + *out_len);
return out;
}
我的目标是基本上将我的图片数据输出到内存中的 png,而不是文件,这样我就可以在我的程序的其他地方使用它,格式就像 png 一样。
最佳答案
大多数参数与传递给 stbi_write_png
的参数相同,它有一个 documentation in the header file :
- 像素是未压缩的图像数据
- stride_bytes 是两个连续行的两个开头之间的字节数:
"stride_in_bytes" is the distance in bytes from the first byte of a row of pixels to the first byte of the next row of pixels.
- x(在
stbi_write_png
中称为w)是图像的宽度 - y(在
stbi_write_png
中称为h)是图像的高度 - n(在
stbi_write_png
中称为comp
)是 channel 数:Each pixel contains 'comp' channels of data stored interleaved with 8-bits per channel, in the following order: 1=Y, 2=YA, 3=RGB, 4=RGBA.
- out_len 是一个输出参数,它返回压缩数据的字节数。
关于c++ - stb_png_to_mem的参数是什么意思?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/59671565/