所以我正在处理一堆 2048x2048 Sprite 表,它们很快就会填满内存。照原样,我正在使用以下方法(通过 Ray Wenderlich)加载纹理:
- (GLuint)setupTexture:(NSString *)fileName
{
CGImageRef spriteImage = [UIImage imageNamed:fileName].CGImage;
if (!spriteImage)
{
NSLog(@"Failed to load image %@", fileName);
exit(1);
}
size_t width = CGImageGetWidth(spriteImage);
size_t height = CGImageGetHeight(spriteImage);
GLubyte * spriteData = (GLubyte *) calloc(width*height*4, sizeof(GLubyte));
CGContextRef spriteContext = CGBitmapContextCreate(spriteData, width, height, 8, width*4,CGImageGetColorSpace(spriteImage), kCGImageAlphaPremultipliedLast);
CGContextDrawImage(spriteContext, CGRectMake(0, 0, width, height), spriteImage);
CGContextRelease(spriteContext);
GLuint texName;
glGenTextures(1, &texName);
glBindTexture(GL_TEXTURE_2D, texName);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, spriteData);
GLenum err = glGetError();
if (err != GL_NO_ERROR)
NSLog(@"Error uploading texture. glError: 0x%04X", err);
free(spriteData);
return texName;
}
所以我的问题是,我如何从 CGImage 中丢弃 alpha 信息,然后将图像“下采样”到每个像素更少的位数,最后将它告诉 OpenGL?
最佳答案
我使用这段代码将 CGContextDrawImage
写入的数据转换为 RGB565。它使用优化的 NEON 代码在支持 NEON 的设备上一次处理 8 个像素(每个运行 armv7 代码的 iOS 设备都有这样的芯片)。您看到的 data
指针与您的 spriteData
指针相同,我只是懒得重命名它。
void *temp = malloc(width * height * 2);
uint32_t *inPixel32 = (uint32_t *)data;
uint16_t *outPixel16 = (uint16_t *)temp;
uint32_t pixelCount = width * height;
#ifdef __ARM_NEON__
for(uint32_t i=0; i<pixelCount; i+=8, inPixel32+=8, outPixel16+=8)
{
uint8x8x4_t rgba = vld4_u8((const uint8_t *)inPixel32);
uint8x8_t r = vshr_n_u8(rgba.val[0], 3);
uint8x8_t g = vshr_n_u8(rgba.val[1], 2);
uint8x8_t b = vshr_n_u8(rgba.val[2], 3);
uint16x8_t r16 = vmovl_u8(r);
uint16x8_t g16 = vmovl_u8(g);
uint16x8_t b16 = vmovl_u8(b);
r16 = vshlq_n_u16(r16, 11);
g16 = vshlq_n_u16(g16, 5);
uint16x8_t rg16 = vorrq_u16(r16, g16);
uint16x8_t result = vorrq_u16(rg16, b16);
vst1q_u16(outPixel16, result);
}
#else
for(uint32_t i=0; i<pixelCount; i++, inPixel32++)
{
uint32_t r = (((*inPixel32 >> 0) & 0xFF) >> 3);
uint32_t g = (((*inPixel32 >> 8) & 0xFF) >> 2);
uint32_t b = (((*inPixel32 >> 16) & 0xFF) >> 3);
*outPixel16++ = (r << 11) | (g << 5) | (b << 0);
}
#endif
free(data);
data = temp;
关于ios - iOS 纹理加载上的 OpenGL ES - 我如何从 RGBA8888 .png 文件获取 RGB565 纹理?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/7930148/