Question

我正在尝试为屏幕外帧缓冲区绘制半透明颜色的线条，使用glCopyTexSubImage2D将其复制到纹理中，然后将该纹理绘制到屏幕帧缓冲区。我尝试了很多配置但只有一条不透明的线。

有关更多信息，请参阅我设置OpenGL的方法：

首先，我将EAGLView子类化，然后添加一个屏幕外的帧缓冲区：

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

glGenRenderbuffersOES(1, &offscreenRenderbuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, offscreenRenderbuffer);

glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_RGBA8_OES, kTextureOriginalSize, kTextureOriginalSize);
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_RENDERBUFFER_OES, offscreenRenderbuffer); 

glGenRenderbuffersOES(1, &offscreenDepthBuffer);
glBindRenderbufferOES(GL_RENDERBUFFER_OES, offscreenDepthBuffer);
glRenderbufferStorageOES(GL_RENDERBUFFER_OES, GL_DEPTH_COMPONENT16_OES, kTextureOriginalSize, kTextureOriginalSize);
glFramebufferRenderbufferOES(GL_FRAMEBUFFER_OES, GL_DEPTH_ATTACHMENT_OES, GL_RENDERBUFFER_OES, offscreenDepthBuffer);

// Offscreen framebuffer texture target
glGenTextures(1, &offscreenRenderTexture);
glBindTexture(GL_TEXTURE_2D, offscreenRenderTexture);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR); 
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR); 

unsigned char * data = (unsigned char *)malloc( kTextureOriginalSize * kTextureOriginalSize * 4 ); 
memset( data,0xff, kTextureSizeWidth * kTextureSizeHeight * 4 );
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, kTextureOriginalSize, kTextureOriginalSize, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);    

glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, offscreenRenderTexture, 0);

glEnable( GL_TEXTURE_2D);
glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
glEnableClientState(GL_VERTEX_ARRAY);
glEnable(GL_BLEND);
glBlendFunc( GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA );

将数据从屏幕外帧缓冲区复制到纹理

glBindTexture( GL_TEXTURE_2D, offscreenRenderTexture);
glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, kTextureOriginalSize, kTextureOriginalSize);

我使用glColor4f在绘图前更改颜色的alpha。

感谢您的帮助！

Answer 1

我找到了答案：

首先，我需要将alpha设置为小：像0.1一样看效果。
其次，glBlendFunc()有效仅在活动帧缓冲区上，所以我需要两次致电glBlendFunc() 屏幕外和屏幕上都有帧缓冲区。或者实际上，我所做的是渲染时禁用GL_BLEND 纹理到屏幕上的帧缓冲。

如何绘制一个半透明三角形到后台缓冲区再渲染它？

1 个答案: