Sub-pixeling

[anon_81132541]

It seems that the coords in the Rect of every GUI.* function are rounded to nearest integer before rendering.

So, for example, a sprite wouldn’t move smoothly across the screen?

How do you do it? Move it using the GUI.matrix?

[Eric5h5]

@""

So, for example, a sprite wouldn’t move smoothly across the screen?

It would, since a pixel is the smallest unit that can be displayed anyway. If you have problems with smoothness, make sure vsync is on, so the display updating is synced to the monitor.

–Eric

[anon_81132541]

Yeah, but I think that internally the graphics API accepts floating point numbers, and in fact there is a difference in the way the graphics card treats 40 vs 40.5322.

This is an explanation I have found:

Fundamentally, there is no such thing as drawing to a fractional pixel location. Either you draw to a pixel, or you don’t. Pixels are discrete, integer things.

When you ask for a fractional position, the graphics card emulates this by filtering your texture. It can’t actually draw values from your texture to half way in between two screen pixels, but it can draw to a single screen pixel using a value that it computes by filtering from half way in between two pixels of your texture.

Usually this is a good thing because it makes everything appear to move with sub-pixel accuracy. It’s particularly important for making 3D rendering look good.

Other times, though, you might not want this filtering. A prime example being if your texture actually contains several different images arranged next to each other: in that case you will get visual errors if the card tries to filter past the edge of one image to include data from the next one along.

Solution: if you don’t want filtering, don’t draw at sub-pixel positions. Round your coordinates to integers before you draw the sprite.

So, the difference is in the graphics cards doing a filtering when fetches the texture color.

That’s why you have to sum 0.5 when passing the UV coords to DirectX, because it takes the pixel origin at its center and if you dont do that your texture gets filtered.

This filtering of course is desirable when you want your sprite appear to move smoother around your screen.

[Brian-Kehrer]

He’s right, Eric.

I did it like this-

take this code

Window (i,Rect (theX,theY,100,28), titleWin,"");

replace it with this.

var pos = new Vector3(theX,theY,0);
var q = new Quaternion(0,0,0,1);
var s = new Vector3(1,1,1);
var tMatrix : Matrix4x4 = Matrix4x4.TRS(pos, q, s);
GUI.matrix = tMatrix;
Window (i,Rect (0,0,100,28), titleWin,"");

perfect sub-pixeling…

[yoyo]

Cool, thanks Brian. Note that you can create the matrix like this too …

var tMatrix : Matrix4x4 = Matrix4x4.identity;
tMatrix[0,3] = theX;
tMatrix[1,3] = theY;