从GraphicBuffer读取时出现意外的像素数据布局 [英] Unexpected pixel data layout when reading from GraphicBuffer
问题描述
我目前正在原生的Android框架中使用一个平台，我使用GraphicBuffer分配内存，然后从中创建一个EGLImage。这是一个纹理在我渲染的OpenGL（使用一个简单的全屏四边形）。
I am currently working on a platform in the native Android framework where I use GraphicBuffer to allocate memory and then create an EGLImage from it. This is then used as a texture in OpenGL which I render to (with a simple fullscreen quad).
问题是当我从GraphicBuffer读取渲染的像素数据，我期望它是在存储器中的线性RGBA格式，但结果是一个纹理，包含图像的三个平行的较小的克隆和重叠的像素。也许这个描述没有说多少，但重点是实际的像素数据有意义，但内存布局似乎是除线性RGBA之外的东西。我假设这是因为图形驱动程序存储的像素的内部格式，而不是线性RGBA。
The problem is when I read the rendered pixel data from the GraphicBuffer, I expect it to be in a linear RGBA format in memory but the result is a texture which contains three parallell smaller clones of the image and with overlapping pixels. Maybe that description doesn't say much but the point is the actual pixel data makes sense but the memory layout seems to be something other than linear RGBA. I assume this is because the graphics drivers store the pixels in an internal format other than linear RGBA.
如果我渲染到一个标准的OpenGL纹理和读取glReadPixels一切工作正常，所以我假设问题在于我的自定义内存分配与GraphicBuffer。
If I render to a standard OpenGL texture and read with glReadPixels everything works fine, so I assume the problem lies with my custom memory allocation with GraphicBuffer.
如果原因是驱动程序的内部存储器布局，有任何方式强制布局线性RGBA？我试过大部分的使用标志提供给GraphicBuffer构造函数没有成功。如果没有，是否有一种方法在着色器中以不同的方式输出数据以取消内存布局？
If the reason is the drivers' internal memory layout, is there any way of forcing the layout to linear RGBA? I have tried most of the usage flags supplied to the GraphicBuffer constructor with no success. If not, is there a way to output the data differently in the shader to "cancel out" the memory layout?
我正在为Nexus 5创建Android 4.4.3。
I am building Android 4.4.3 for Nexus 5.
//Allocate graphicbuffer
outputBuffer = new GraphicBuffer(outputFormat.width, outputFormat.height, outputFormat.bufferFormat,
GraphicBuffer::USAGE_SW_READ_OFTEN |
GraphicBuffer::USAGE_HW_RENDER |
GraphicBuffer::USAGE_HW_TEXTURE);
/* ... */
//Create EGLImage from graphicbuffer
EGLint eglImageAttributes[] = {EGL_WIDTH, outputFormat.width, EGL_HEIGHT, outputFormat.height, EGL_MATCH_FORMAT_KHR,
outputFormat.eglFormat, EGL_IMAGE_PRESERVED_KHR, EGL_FALSE, EGL_NONE};
EGLClientBuffer nativeBuffer = outputBuffer->getNativeBuffer();
eglImage = _eglCreateImageKHR(display, EGL_NO_CONTEXT, EGL_NATIVE_BUFFER_ANDROID, nativeBuffer, eglImageAttributes);
/* ... */
//Create output texture
glGenTextures(1, &outputTexture);
glBindTexture(GL_TEXTURE_2D, outputTexture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_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);
_glEGLImageTargetTexture2DOES(GL_TEXTURE_2D, eglImage);
/* ... */
//Create target fbo
glGenFramebuffers(1, &targetFBO);
glBindFramebuffer(GL_FRAMEBUFFER, targetFBO);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, outputTexture, 0);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
/* ... */
//Read from graphicbuffer
const Rect lockBoundsOutput(quadRenderer->outputFormat.width, quadRenderer->outputFormat.height);
status_t statusgb = quadRenderer->getOutputBuffer()->lock(GraphicBuffer::USAGE_SW_READ_OFTEN, &result);
推荐答案
我设法自己找到答案，一直。简单的原因是，虽然我正在渲染一个480x1080的纹理，分配的内存填充为640x1080，所以我只需要删除每一行后的填充和输出纹理有意义。
I managed to find the answer myself and I was wrong all along. The simple reason was that although I was rendering a 480x1080 texture the memory allocated was padded to 640x1080 so I just needed to remove the padding after each row and the output texture made sense.
这篇关于从GraphicBuffer读取时出现意外的像素数据布局的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
