OpenGL到iPhone上的视频

Question

我目前正在开发一个项目,将物理模拟转换为iPhone本身的视频.

为此,我现在使用两个不同的循环.第一个循环在块中运行,其中AVAssetWriterInput对象轮询EAGLView以获取更多图像.EAGLView提供存储它们的数组中的图像.

另一个循环是实际模拟.我已经关闭了模拟计时器,并且每次都使用预先指定的时间差来调用tick.每次调用tick时,我都会在交换缓冲区后在EAGLView的交换缓冲区方法中创建一个新图像.然后将此图像放在AVAssetWriter轮询的数组中.

还有一些杂项代码,以确保数组不会太大

所有这一切都很好,但非常慢.

我在做什么,从概念上讲,导致整个过程比它可能更慢？另外,有没有人知道从glReadPixels获取Open GL图像的更快方法？

Answer 1

视频内存的设计使得写入速度快，读取速度慢。这就是我执行纹理渲染的原因。这是我创建的用于将场景渲染为纹理的完整方法（有一些自定义容器，但我认为用您自己的容器替换它们非常简单）：

-(TextureInf*) makeSceneSnapshot {
    // create texture frame buffer
    GLuint textureFrameBuffer, sceneRenderTexture;

    glGenFramebuffersOES(1, &textureFrameBuffer);
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, textureFrameBuffer);

    // create texture to render scene to
    glGenTextures(1, &sceneRenderTexture);
    glBindTexture(GL_TEXTURE_2D, sceneRenderTexture);

    // create TextureInf object
    TextureInf* new_texture = new TextureInf();
    new_texture->setTextureID(sceneRenderTexture);
    new_texture->real_width = [self viewportWidth];
    new_texture->real_height = [self viewportHeight];

    //make sure the texture dimensions are power of 2
    new_texture->width = cast_to_power(new_texture->real_width, 2);
    new_texture->height = cast_to_power(new_texture->real_height, 2);

    //AABB2 = axis aligned bounding box (2D)
    AABB2 tex_box;

    tex_box.p1.x = 1 - (GLfloat)new_texture->real_width / (GLfloat)new_texture->width;
    tex_box.p1.y = 0;
    tex_box.p2.x = 1;
    tex_box.p2.y = (GLfloat)new_texture->real_height / (GLfloat)new_texture->height;
    new_texture->setTextureBox(tex_box);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA,  new_texture->width, new_texture->height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
    glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, sceneRenderTexture, 0);

    // check for completness
    if(glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES) != GL_FRAMEBUFFER_COMPLETE_OES) {
        new_texture->release();
        @throw [NSException exceptionWithName: EXCEPTION_NAME
                                       reason: [NSString stringWithFormat: @"failed to make complete framebuffer object %x", glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES)]
                                     userInfo: nil];
        new_texture = nil;
    } else {
        // render to texture
        [self renderOneFrame];
    }

    glDeleteFramebuffersOES(1, &textureFrameBuffer);

    //restore default frame and render buffers
    glBindFramebufferOES(GL_FRAMEBUFFER_OES, _defaultFramebuffer);
    glBindRenderbufferOES(GL_RENDERBUFFER_OES, _colorRenderbuffer);
    glEnable(GL_BLEND);         
    [self updateViewport];      
    glMatrixMode(GL_MODELVIEW);


    return new_texture;
}

当然，如果您一直在进行快照，那么您最好只创建一次纹理帧和渲染缓冲区（并为它们分配内存）。