QImage的坐标系

(0,0)-------
|           |
|           |
|           |
|           |
|--------(1,1)

验证代码：

int width = 20, height = 10;
int size = width * height;
unsigned char* buffer = (unsigned char*)malloc(size);
if (!buffer)
{
    return;
}
// 0黑色 255白色
memset(buffer, 0, size);
// 第一象限灰色
for (int i = 0;i < height / 2;i++)
{
    for (int j = 0;j < width / 2;j++)
    {
        buffer[i * width + j] = 100;
    }
}

view->showA8Texture(width, height, buffer, size);
free(buffer);

可以看到第一象限在左上角，符合坐标系的预期。

FT_Bitmap

FT_Bitmap的结构

typedef struct  FT_Bitmap_
{
unsigned int    rows;
unsigned int    width;
int             pitch;
unsigned char*  buffer;
unsigned short  num_grays;
unsigned char   pixel_mode;
unsigned char   palette_mode;
void*           palette;

} FT_Bitmap;

buffer指向的就是纹理内存，这个纹理内存的坐标系和QImage一致，都是左上角是(0,0)

cocos

cocos2dx 中对bitmap的纹理有个转换

// 绘制的起始坐标
int iX = posX;
int iY = posY;
for (long y = 0; y < bitmapHeight; ++y){
    long bitmap_y = y * bitmapWidth;
    for (int x = 0; x < bitmapWidth; ++x){
        unsigned char cTemp = bitmap[bitmap_y + x];
        // the final pixel
        int dest_idx = (iX + (iY * FontAtlas::CacheTextureWidth));
        dest[dest_idx] = cTemp;
        CCLOG("bitmap:%d => dest:%d", bitmap_y + x, dest_idx);
        iX += 1;
    }
    iX  = posX;
    iY += 1;
}

width:43, height:86
bitmap:0 => dest:513 = (1 + (1*512))
bitmap:1 => dest:514
bitmap:2 => dest:515
bitmap:3 => dest:516
bitmap:4 => dest:517
bitmap:5 => dest:518
bitmap:6 => dest:519
bitmap:7 => dest:520
bitmap:8 => dest:521
bitmap:9 => dest:522
bitmap:10 => dest:523
bitmap:11 => dest:524
bitmap:12 => dest:525
bitmap:13 => dest:526
bitmap:14 => dest:527
bitmap:15 => dest:528

把纹理copy到了大纹理里面，并且有(1,1)的偏移，从下图看的更加清晰：

使用到QImage去查看纹理数据

不要被OpenGL的坐标系迷惑，engine会自动处理坐标系问题