从另一个线程中保存tiff文件中的opengl纹理

I'm trying to save a texture in tiff file from an other thread. But the only result i get is a white picture, I think it come from the glcontext ( because it's not possible to have one glcontext for several thread). That's why i've tried to create two glcontext and share the display context. But still i don't have the gl texture. I can't get the texture from the second opengl context . I'm tring to do that because at the end the texture will be a video stream from a camera . Here is my context creation :I'm trying to save a texture in tiff file from