差的opengl图像处理性能 [英] Poor opengl image processing performance
问题描述
我想使用opengl做一些简单的图像处理。因为我找不到任何好的图书馆，我一直在努力做我自己的解决方案。
I'm trying to do some simple image processing using opengl. Since I couldn't find any good library that does this alrdy I've been trying to do my own solution.
我只想在gpu上组成几个图像然后读回他们。但是我的实现的性能看起来几乎等于它在cpu上做的事情... ...是错误的...
I simply want to compose a few images on the gpu and then read them back. However the performance of my implementation seems almost equal to what it takes do on the cpu... something is wrong...
我试图遵循最佳实践我在网上找到了。但仍然做错了。
I've tried to follow the best practices I've found on the net. But still it's doing something wrong.
我已尝试删除所有不相关的代码。
I've tried removing all the irrelevant code.
？
int image_width = 1280;
int image_height = 720;
int image_size = image_width * image_height;
class texture
{
public:
texture()
{
glGenTextures(1, &texture_);
bind();
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, image_width, image_height, 0, GL_BGRA, GL_UNSIGNED_BYTE, NULL);
}
~texture(){ glDeleteTextures(1, &texture_); }
void bind(){ glBindTexture(GL_TEXTURE_2D, texture_); }
GLuint handle() { return texture_; }
private:
GLuint texture_;
};
typedef std::shared_ptr<texture> texture_ptr;
class pixel_buffer // pixel buffer with associated texture
{
public:
pixel_buffer()
{
glGenBuffersARB(1, &pbo_);
bind_pbo();
glBufferDataARB(GL_PIXEL_UNPACK_BUFFER_ARB, image_size, 0, GL_STREAM_DRAW);
}
~pixel_buffer(){ glDeleteBuffers(1, &pbo_); }
void begin_write(void* src)
{
texture_.bind();
glBindBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, pbo_);
glBufferDataARB(GL_PIXEL_UNPACK_BUFFER_ARB, image_size, 0, GL_STREAM_DRAW);
void* ptr = glMapBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, GL_WRITE_ONLY);
assert(ptr);
memcpy(ptr, src, image_size);
glUnmapBuffer(GL_PIXEL_UNPACK_BUFFER);
}
void end_write()
{
bind_texture();
bind_pbo();
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, image_width, image_height, GL_BGRA, GL_UNSIGNED_BYTE, BUFFER_OFFSET(0));
unbind_pbo();
}
void begin_read(GLuint buffer)
{
glReadBuffer(buffer);
glBindBuffer(GL_PIXEL_PACK_BUFFER_ARB, pbo_);
glBufferData(GL_PIXEL_PACK_BUFFER_ARB, image_size, NULL, GL_STREAM_READ);
glReadPixels(0, 0, image_width, image_height, GL_BGRA, GL_UNSIGNED_BYTE, BUFFER_OFFSET(0));
}
void end_read(void* dest)
{
void* ptr = glMapBuffer(GL_PIXEL_PACK_BUFFER_ARB, GL_READ_ONLY);
memcpy(dest, ptr, image_size);
glUnmapBuffer(GL_PIXEL_PACK_BUFFER_ARB);
unbind_pbo();
}
void bind_pbo(){ glBindBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, pbo_); }
void unbind_pbo(){ glBindBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, pbo_); }
void bind_texture() { texture_.bind(); }
GLuint texture_handle() { return texture_.handle(); }
private:
texture texture_;
GLuint pbo_;
};
typedef std::shared_ptr<pixel_buffer> pixel_buffer_ptr;
class frame_buffer// frame buffer with associated pixel buffer
{
public:
frame_buffer()
{
glGenFramebuffersEXT(1, &fbo_);
bind();
pbo_.bind_texture();
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, pbo_.texture_handle(), 0);
}
~frame_buffer() { glDeleteFramebuffersEXT(1, &fbo_); }
void bind() { glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo_); }
void unbind() { glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); }
void begin_read()
{
bind();
pbo_.begin_read(GL_COLOR_ATTACHMENT0_EXT);
}
void end_read(void* dest)
{
pbo_.end_read(dest);
unbind();
}
private:
pixel_buffer pbo_;
GLuint fbo_;
};
typedef std::shared_ptr<frame_buffer> frame_buffer_ptr;
struct image_processor::implementation
{
void compose(const std::vector<image_ptr>& images)
{
// END PREVIOUS READ
if(reading_fbo_)
{
image_ptr result_image = std::make_shared<image>(image_size);
reading_fbo_->end_read(result_image->data());
output_.push(reading_result_image_);
reading_fbo_ = nullptr;
}
// END PREVIOUS WRITE
frame_buffer_ptr written_fbo;
if(!writing_pbo_group_.empty())
{
// END
written_fbo = get_fbo();
written_fbo->bind();
glClear(GL_COLOR_BUFFER_BIT);
for(size_t n = 0; n < writing_pbo_group_.size(); ++n)
{
writing_pbo_group_[n]->end_write();
writing_pbo_group_[n]->bind_texture();
quad_->draw(); // DRAW FULLSCREEN QUAD
}
written_fbo->unbind();
writing_pbo_group_.clear();
}
// BEGIN NEW WRITE
if(!images.empty())
{
for(size_t n = 0; n < images.size(); ++n)
{
auto pbo = get_pbo();
pbo->begin_write(images[n]->data());
writing_pbo_group_.push_back(pbo);
}
}
// BEGIN NEW READ
if(written_fbo)
{
written_fbo->begin_read();
reading_fbo_ = written_fbo;
}
}
pixel_buffer_ptr get_pbo()
{
if(pbo_pool_.empty())
pbo_pool_.push_back(std::make_shared<pixel_buffer>());
auto pbo = pbo_pool_.front();
pbo_pool_.pop_front();
return pixel_buffer_ptr(pbo.get(), [=](pixel_buffer*){pbo_pool_.push_back(pbo);});
}
frame_buffer_ptr get_fbo()
{
if(fbo_pool_.empty())
fbo_pool_.push_back(std::make_shared<frame_buffer>());
auto fbo = fbo_pool_.front();
fbo_pool_.pop_front();
return frame_buffer_ptr(fbo.get(), [=](frame_buffer*){fbo_pool_.push_back(fbo);});
}
std::vector<pixel_buffer_ptr> writing_pbo_group_;
frame_buffer_ptr reading_fbo_;
std::deque<pixel_buffer_ptr> pbo_pool_;
std::deque<frame_buffer_ptr> fbo_pool_;
};
编辑：
大多数cpu时间似乎花在了begin_write（）;
Did some profiling. Most cpu time seems to be spent in begin_write();
虽然...看不到任何错误...
Can't see anything wrong with it though...
void begin_write(void* src)
{
texture_.bind();
glBindBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, pbo_);
glBufferDataARB(GL_PIXEL_UNPACK_BUFFER_ARB, image_size, 0, GL_STREAM_DRAW);
void* ptr = glMapBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, GL_WRITE_ONLY);
assert(ptr);
memcpy(ptr, src, image_size);
glUnmapBuffer(GL_PIXEL_UNPACK_BUFFER);
}
推荐答案
您的瓶颈是内存传输从CPU到GPU。 GPU允许您在需要对存储在GPU内存中的相同小量数据执行许多并行计算（例如，每秒绘制相同的场景30帧）时提高性能。当您需要从主内存和GPU内存来回传输数据时，大多数时间都是浪费在这一点上的。
Your bottleneck is the memory transfer from the CPU to the GPU. GPU allows you to boost performance when you need to do many parallel calculations on the same small amount of data that is stored in the GPU memory (for example draw the same scene 30 frames per second). When you need to transfer data back and forth from the main memory and GPU memory, most of the time is wasted on exactly that.
这篇关于差的opengl图像处理性能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！
