Water in a terrain engine

[MrShoe]

I have a terrian engine set up, and i want to add water. I triwed to do this by simply having a semi transparent quad textured drawn at a certain height... This isnt bad except for the fact that there is REALLY bad jittering effect when the water meets the terrain. The waters edge jitters very badly there. does anyone know how to fix this.

[Spiral Man]

a) increase the depth of your depth buffer if you can.

b) draw the water slightly higher, so it is further from terrain polygons that are roughly parallel to it.

c) increase the angle of the terrain polygons at the waters edge, so they are more perpendicular to the water (this goes with b)

d) use glPolygonOffset when you draw the water, might work...

[rixed]

for point a) :
Isn't it rather decreasing the depth of zbuffer that would give a more precise zbuffer on the range covered ? Or did I missed something ? For me, the lesser zmax-zmin, the better the precision. Am I wrong ?

[JML]

Originally posted by rixed:
for point a) :
Isn't it rather decreasing the depth of zbuffer that would give a more precise zbuffer on the range covered ? Or did I missed something ? For me, the lesser zmax-zmin, the better the precision. Am I wrong ?

Correct, but 'increasing the depth' means increasing the number of available bits (via a different pixelformat) in this case I think.
And yes, mapping a smaller range of depth values to the available depth bits will also improve accuracy.

BTW: the difference between zmax and zmin is not the only important factor, it is also the ratio between zmax and zmin:
zmin = 100, zmax = 199 is creates better accuracy than zmin = 1, zmax = 100 even if the difference is 99 in both cases.

HTH

Jean-Marc

[rixed]

OK!

I usually set zmin=1, so I will fix it since its not relevant in many case if its 1 or 10 or even 100.

I didn't know about this ratio thing. I will watch at the z calculations in the gl specs to understand why.

thanks

[Heaven]

I've got the same problem and am using the same method as you are until I get a textured wavy surface going. When I zoomed my camera in and scaled my view down to keep everything the same size it helped enormously.

Try that and see what you think. Set your eyepoint closer to the scene, and render the scene smaller to keep it to scale. Instead of "zooming in" you're just increasing the resolution so to speak.

I think.

Care,
Chris

[Spiral Man]

just to clarify, yes, i did mean increase the bit depth of the depth buffer...

[MrShoe]

Thanks all, but i figured it out, there is a much simpler way of fixing this, just use multiple quads in a grid. Having just one huge quad covering the entire map was the thing stuffing it up... So now i have a bunch of smaller quads...

[Nervus]

the Z-Buffer artifacts can be avoided in two ways:
1) By increasing the zbuffer bit depth
2) by setting the near plane a value bigger than 1, preferably set it 5 or 10 depending on how close do you want to look at the terrain
if the value is too big , you'll encounter some unwanted nearplane clipping...

good luck.

[Keermalec]

Mr. Shoe, more quads means a slower engine. You can fix your problem by using only a single quad and decreasing the ratio between the near and far clipping planes. For example:

gluPerspective(fov,ratio,1.0f,100.0f);

will give much better results than:

gluPerspective(fov,ratio,0.1f,1000.0f);

Try it