Texture UV Question

Blitz3D Forums/Blitz3D Programming/Texture UV Question

KuRiX

(Posted 2005) [#1]

Hi friends. I have another question about cpu consuming and efficiency.

Suppose you have a quad polygon (2 triangles of course) and you decide to texure it with some "floor texture". If i decide to repeat the texture 4x4 times in the same quad, does the computer need more time to render the quad?

For what i know, i think that the speed should be the same, because the pixels rendered to the screen are the same... but i am not sure... any 3d guru knows the answer?

Ross C

(Posted 2005) [#2]

Well, i know my my card, if a texture is over tiled, it does slow down the rendering. Best, if you want more tiling, to use a larger texture, with the tiled pattern on it.

Finjogi

(Posted 2005) [#3]

Only CPU load should come from scaling UV coordinates, that is if you use ScaleTexture(), but even that could be done in GPU.. I'm not sure which way DX7 does that. If you do tiling in your modeling phase, there is no extra CPU work in runtime.

GPU however needs to read a tiled texture more often and that could slow you down little bit. Problem lies in when GPU reads BIG texture and only draws it to small area, like 512*512 -> 16*16 pixel area in to the screen. Even then mip mapping and texture cache should take care of it. (mip mapping -> smaller, pre shrinked copies of main texture -> 512 -> 256 -> 128, 64...2)

Mustang

(Posted 2005) [#4]

Don't worry kurix, that would be quite okay to do. Much better and faster than having for example four quads and four uv-sets for example. Tiling/scaling of textures is one of the basic 3D-operations so every card is designed to do it really fast.

KuRiX

(Posted 2005) [#5]

Great, thanks!

John Pickford

(Posted 2005) [#6]

The texture is sampled per pixel (on screen) so only the size of the triangle on screen matters. U\V coords are irrelevant.

I think Ross C is wrong up there.

So long as the texture is in VRAM its size or how its scaled makes no difference.

Finjogi

(Posted 2005) [#7]

Technically it matters :)
See how poorly texture tiling does without mipmapping :)

Graphics3D 640,480,32,2    
        
cam=CreateCamera()    
PositionEntity cam,0,0,-200    
    
l=CreateLight()    

model = CreateCube() 
ScaleEntity model, 100,100,100  

tex = CreateTexture(512, 512)
SetBuffer TextureBuffer(tex)

For y=0 To 512
	For x=0 To 512
		Color x/2, y/2, 128
		Plot x,y
	Next
Next

SetBuffer BackBuffer()

EntityTexture model, tex  


Color 255,255,255
    
ts#=1.0
While Not KeyHit(1)   

	ts# = ts# - 0.0002
	ScaleTexture tex, ts#, ts#

	TurnEntity model, 0, 0, 0.1 
     
 	RenderWorld    
   
   
	If (frames=10) Then
		oldtime = time
		time = MilliSecs() 
  	        ms = time - oldtime 
 		frames=0
	EndIf

frames = frames + 1
 
 Text 0,0,"ms / 10 frames " + ms   
 Text 0,10,"texturescale " + ts#   
 Flip 0    
    
Wend
End

jhocking

(Posted 2005) [#8]

Well, i know my my card, if a texture is over tiled, it does slow down the rendering.

What card is this? On everything I've ever worked with it's best (or at least "renders fastest"; "best" is a relative term) to tile textures by scaling the UVs, as opposed to larger tiled image or tessalating the plane.

Ross C

(Posted 2005) [#9]

Well, tile is really small, and there definetly is a slowdown. I might not have been using mipmapping, but extreme tiling does you no favours. I'll try get a sample.

KuRiX

(Posted 2005) [#10]

Of course i used the 4x4 tiling to set and example, but i am asking about 50x2 tiling and so...

I must say i have seen slowdowns with too much tiling... (200 more less)