OpenGL 3.2上的每渲染目标混合

Question

我目前在目标平台上受限于OpenGL 3.2，而且我无法访问glBlendFunci。我可以使用glBlendFunc或glBlendFuncSeparate。例如，在OpenGL 4.4上，我使用glBlendFunci获得了下面的代码。如何在OpenGL 3.2上以相同的结果替换它？如果创建单独的通行证会更好还是会损害性能？

glBindFramebuffer(GL_FRAMEBUFFER, framebuffer);

// generate accum texture
glBindTexture(GL_TEXTURE_2D, accum);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA32F, w, h, 0, GL_RGBA, GL_FLOAT, 0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, accum, 0);

// generate reveal texture
glBindTexture(GL_TEXTURE_2D, reveal);
glTexImage2D(GL_TEXTURE_2D, 0, GL_R32F, w, h, 0, GL_RED, GL_FLOAT, 0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT1, GL_TEXTURE_2D, reveal, 0);


// blending
glBlendFunci(0, GL_ONE, GL_ONE);
glBlendFunci(1, GL_ZERO, GL_ONE_MINUS_SRC_ALPHA);