Multiple sample FBO problem in line drawing

OpenGL OpenGL: Advanced Coding
1

Hi All,

I encountered an annoying problem when using multiple-sampled FBO. That is, I found when setting the FBO’s multiple-sampling mode to 8x on my Nvidia 7800 GTX Go, any drawn line will be thicker than desired.

For better explanation, here are two screenshots created using Nvidia SDK sample

Image using FBO without MSAA

Image using FBO with 8x MSAA

as you can see, the line width is changed. I wish it’s a driver bug.

(Sorry for the website justupit may show you ADs)

So I am wondering if anyone experienced similar problem before and any suggestions are welcome.

Thanks.

2

I guess it’s the way how MSAA FBO works. For very thin and high-contrast primitives, it’s always tricky.

But it seems that rendering using a MSAA FBO is still not same as Non-FBO based MSAA rendering since there is no such problem when directly render to back-buffer in MASS mode. Wish eventually the vendors can make them same …

3

What you are seeing is correct. Move the line up or down by half a pixel if you want it to be drawn exactly on one row of pixels.

4

Thanks and I will give a try :slight_smile: