我正在编写一个小型库来与
Linux的帧缓冲抽象接口.我的所有显卡都使用相同的像素格式(每个通道一个八位字节,四个通道,BGRA排序),所以到目前为止,库只采用这种格式.但是,framebuffer API提供像素格式数据,如果我希望库在任何Linux帧缓冲区上工作,我必须使用它.你不需要知道帧缓冲如何回答这个问题(我希望),只是有点小提琴我不熟练.这是我的标题中提供的像素格式信息:
/* Interpretation of offset for color fields: All offsets are from the right,
* inside a "pixel" value, which is exactly 'bits_per_pixel' wide (means: you
* can use the offset as right argument to <<). A pixel afterwards is a bit
* stream and is written to video memory as that unmodified.
*
* For pseudocolor: offset and length should be the same for all color
* components. Offset specifies the position of the least significant bit
* of the pallette index in a pixel value. Length indicates the number
* of available palette entries (i.e. # of entries = 1 << length).
*/
struct fb_bitfield {
__u32 offset; /* beginning of bitfield */
__u32 length; /* length of bitfield */
__u32 msb_right; /* != 0 : Most significant bit is */
/* right */
};
/* snip */
struct fb_var_screeninfo {
/* snip */
__u32 bits_per_pixel; /* guess what */
__u32 grayscale; /* 0 = color, 1 = grayscale, */
/* >1 = FOURCC */
struct fb_bitfield red; /* bitfield in fb mem if true color, */
struct fb_bitfield green; /* else only length is significant */
struct fb_bitfield blue;
struct fb_bitfield transp; /* transparency */
__u32 nonstd; /* != 0 Non standard pixel format */
/* snip */
};
我需要将一个使用上述信息格式化的像素写入四个字符(R,G,B和A)的字符数组中.我做过这个误导的尝试看起来像这样:
long pxl = 0;
/* downsample each channel to the length (assuming its less than 8 bits) */
/* with a right-shift, then left shift it over into place */
/* haven't done anything with fb_bitfield.msb_right */
pxl |= (r >> (8 - vinfo.red.length)) << vinfo.red.offset;
pxl |= (g >> (8 - vinfo.green.length)) << vinfo.green.offset;
pxl |= (b >> (8 - vinfo.blue.length)) << vinfo.blue.offset;
pxl |= (a >> (8 - vinfo.transp.length)) << vinfo.transp.offset;
fb[xy2off(x, y)] = /* umm... */;
/* little endian, big endian? Can I just assign here? */
xy2off将坐标转换为索引. fb是指向帧缓冲区的指针(内存映射).
任何人都可以指出我正确的方向转换和分配这些像素?
最佳答案 亲爱的可能不存在的人正在寻找答案:这是我现在看到的那些似乎现在有用的hackish代码:
void pixel(int x, int y, uint8_t r, uint8_t g, uint8_t b, uint8_t a) { int i; long pxl = 0; pxl |= (r >> (8 - vinfo.red.length)) << vinfo.red.offset; pxl |= (g >> (8 - vinfo.green.length)) << vinfo.green.offset; pxl |= (b >> (8 - vinfo.blue.length)) << vinfo.blue.offset; pxl |= (a >> (8 - vinfo.transp.length)) << vinfo.transp.offset; for (i = 0; i < sizeof(long); i++) { fb[xy2off(x, y) + i] = ((char *)(&pxl))[i]; } }
缺少字节序处理,处理msb_right或任何类型的优化.