View Full Version : Choppy movement with floats

11-23-2012, 08:39 AM
The footage pretty much shows the problem:

When I move text slower than a pixel at a time, it doesn't move in subpixels, instead it jumps from pixel to pixel. How can I fix that?
I searched for days, still nothing that could help me with that.
Let me know if I need to show code of some part, I can upload everything, but it'll be a lot to fit in here.

Thanks for the help in advance, hope it will resolve.

11-23-2012, 08:46 AM
Use a multisampled buffer. This will give you sub-pixel coverage, and smooth out the rasterization of your text. The higher the number of samples, the smoother it will become.

Alternatively, you can make the quad 1 pixel larger in each direction, compute the floating point position in screen coordinates where it should appear, and then compare that to the actual GL coords using gl_FragCoord.xy. Use the difference to adjust your texture coordinates.

11-23-2012, 08:51 AM
Thanks for reply, I'm a little concerned about multisampling (performance wise), because DirectX doesn't use it and it has smooth movement out of the box, but OpenGL is not?

11-23-2012, 10:01 AM
Can you explain what you are actually doing?
Is the text in that video a raster image that you are drawing as a textured quad?
Or are the letters a bunch of 3d geometric shapes?

11-23-2012, 10:09 AM
It is textured quads, I move this text by 0.01f each frame.

11-23-2012, 10:44 AM
I just did a test and while the edge of a textured quad is not anti-aliased and will pop pixel to pixel, the texture pixels move smoothly with sub-pixel accuracy.

Are you enabling bi-linear filtering?


11-23-2012, 11:45 AM
I'm using GL_NEAREST, because GL_LINEAR is not what I'm looking for, it makes texture blurry. I want something like D3DTEXF_POINT (DX), it is smooth and have a nearest filtering. Exactly what I need for pixel art and stuff.

11-23-2012, 11:56 AM
Can you verify that GL_LINEAR gives a smoother animation? In spite of how you feel about the fidelity.

I don't see how something can use nearest-neighbor sampling and, at the same time, not pop.

11-23-2012, 11:57 AM
Yeah linear does look smooth, though blurry. =(

And in Direct3D9/10/11 it is nearest with smooth movements
I dunno if that will help, but here is documentation about it: http://msdn.microsoft.com/en-us/library/windows/desktop/bb147229(v=vs.85).aspx

11-23-2012, 12:11 PM
What I mean is: You are seeing an unsightly "pop" when your text image animates (moves). Because 1 pixel from the source image is being drawn at a particular destination pixel one second; then it is drawn in a neighboring destination pixel the next second. That is the "pop". You are moving the texture 1/100th of a pixel on every draw, but the results don't show until you have crossed a mathematical threshold.

That is the nature of nearest-neighbor sampling.
That is the point of it.
There is no sub-pixel distinction.
A source pixel can either live in one destination pixel, or it's neighbor. It can't live in both.

Living in both is what linear does.
(20% in the first pixel, 80% in the second pixel)

11-23-2012, 01:45 PM
Thanks for making it clear, but how is DX doing it I wonder, maybe I could replicate it in shader or something? I just don't have any other way I guess, since I'm going for pixel graphics. =(

11-23-2012, 02:03 PM
I don't think Direct X is doing anything different.

Is your image being drawn 1:1 on the screen?
As opposed to being scaled up or down when drawn to the screen?

11-23-2012, 02:17 PM
Sorry, tested out DX more closely, seems to be almost the same as with OpenGL. Thanks for the help I really appreciate it!