Trying to use glBlitFramebuffer for antialiasing

MacOSX and iOS
1

I am not sure what I am doing wrong, but my texture out of the fbo is like 1/4 the size. To start with, just to get this working I was trying to just do the size 1:1 before I use the GL_LINEAR.

In the “newOpenGLContextCreated”, I am creating a new frame buffer, with:

juce::OpenGLContext* ownerContext = juce::OpenGLContext::getCurrentContext();
fb.initialise(*ownerContext, getWidth(), getHeight());

Later on in the render, to switch to this, I just do:

fb.makeCurrentRenderingTarget();

Then at the end of the render routine, I try doing this:

juce::gl::glBindFramebuffer(juce::gl::GL_READ_FRAMEBUFFER, fb.getFrameBufferID());
juce::gl::glBindFramebuffer(juce::gl::GL_DRAW_FRAMEBUFFER, 0);

juce::gl::glBlitFramebuffer(0,0,getWidth(),getHeight(),0,0,getWidth(),getHeight(),juce::gl::GL_COLOR_BUFFER_BIT,juce::gl::GL_LINEAR);
fb.releaseAsRenderingTarget();

And what I see is 1/4 of the original render in the bottom left of the screen. No amount of playing with glViewport fixes the problem.

Given everything is 1:1 right now, I just have no clue what I have done wrong. (I could see needing to adjust the glViewport once my FBO is twice the size or bigger for downsampling)

Anyone have any idea what I could be doing wrong here?

2

You need to account for DPI scaling manually when rendering into framebuffers.

Most OSs are doing some scaling now. It is ubiquitous on macOS (Retina displays).

3

Is there somewhere else I can determine scaling? I tried this:

openGLContext.getRenderingScale();

And it just said 1.0 when I checked.

4

I see, I was calling it during “newOpenGLContextCreated” and in there it is set to 1, but during the rendering routing, it is 2. I believe it probably makes sense to change the buffer as the window could move between screens and then that target would be different.