Skydome and far clip plane?

[AshMcConnell]

Hi Folks,

I am trying to get a skydome to work using: -

_sceneMgr->setSkyDome(true, "Standard_3", 10, 1, 500, true);

My far clip plane is set to 700, but in certain directions I just see the background colour. If i set the skydome distance to 2000 i don't see it at all, i was under the impression that the clip plane wasn't used when showing the skydome. Is there any way to clip "normal" objects at a lower level than the sky dome distance?

Thanks for your help
All the best,
Ash

[madmarx]

>>>Is there any way to clip "normal" objects at a lower level than the sky dome distance?
Most of the time, it is another way round : skies (skydome/skybox/skyplane) are drawn first with "depth_write off", so you can draw them at distance = 3, and draw the objects at distance = 50, they both will show up (with clip near = 1 and clip far = 2000), with skies behind the objects.

If whatever, you really need to clip normal objects at another level, you can render your viewport in two times. (but i think it's a bad idea) :

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// first draw the far part with your skies.
camera->setNearClipPlane(2000.0);
camera->setNearClipPlane(4000000.0);
viewport->update(); // very inefficient if you have thousands of object because frustum culling will be calculated.
viewport->setClearBuffer(true,FBT_DEPTH); // clean everything but the color
camera->setNearClipPlane(1.0);
camera->setFarClipPlane(2000.0);
viewport->update();
viewport->setClearBuffer(true,FBT_DEPTH|FBT_COLOR);

(everything rendered manually here).
It must be possible too to get directly the renderoperation of the skies for the first render (making it very quickier to execute).

[xadhoom]

I thought it would be more efficient to draw things like a skybox after all solid objects and before all transparent objects. You would save millions of shader operations in best case (if you can´t see the sky because of a wall/floor/terrain).
Ofcourse you have to make a depth test then, but maybe it can be simplified by just checking if there is a value less "max" (I´m not sure if such a depth test actually exists...).
IMHO this would be more performant though especially if you use complex sky rendering like Caelum.

Any experiences about that?

xad

[madmarx]

Well, in case you are in fixed pipeline, I thought it was not anymore that important. I don't use shaders on skybox. But it has certainly fillrate impact with shader, xadhoom you are right.


What you propose could be done with :

sceneManager->_setSkyDome ( true,materialName, curvature,tiling,distance, RENDER_QUEUE_MAIN+1);
for the render queue, it depends on which renderqueue group is used by the transparent objects (could be RENDER_QUEUE_MAIN_7..).

Or even better if you need that bad to save shaders : early z is also possible.
render everything not-transparent with depth_write on, colour-write off (but of course you still need vertex shader, domain shader, hull shader, and geometry shader to be calculated).
RenderableListener allows you to discard any depth_write off / transparent material, and replace material.

If you really really need to save shader, you can also go with deferred shading (like starcraft 2, gta4, & so on), but it is not so 'direct forward' .

[AshMcConnell]

HI Guys,

Thank you both for the replies! I was intending to use either fixed function or perhaps a simple shader to begin with. My approach is get something working - then think about making it fancy .

Would a simple shader that output the simple / unlit texture be the fastest route (in terms of framerate)? I am a graphics newbie really, i have been concentrating on other aspects of my game up to now.

The scene is a simple outdoor racing track, I just want to create a simple background rather than the current clear blue "sky" .

so you can draw them at distance = 3, and draw the objects at distance = 50, they both will show up (with clip near = 1 and clip far = 2000), with skies behind the objects.

Madmarx, sorry to be a newbie, but could you explain a little more about this, I don't quite get what you mean. My current near clip is 0.2 and far is 700 (in order to avoid z fighting problems). How do I keep the skydome within that distance but not in front of the distant objects?

Thanks again!
All the best,
Ash

[madmarx]

quick answer :

1/ concerning your frustum culling:
700 / 0.2 = 700 * 5 = 3500. It's to much IMO for most apps. Try to have a ratio Far/Near at 2000 to get best results.

2/ in your skydome construction, I see that you have only 1 tile. it could be source of the problem.

3/ try
_sceneMgr->setSkyDome(true, "Standard_3", 10, 7, 3, true);
->It will create a skydome with 49 tiles at distance 3.
-> 0.2(near)< 3(distance skydome) <700(far) so it will be visible.
->your skydome is drawn first (because of the 6th parameter).
-> other objects will be drawn after it. Normally they wouldn't show up if object_distance>skydomedistance.
-> so when drawing the skydome, you need to use a special material, which will simulate infinite distance.
-> the material must not write in the depht/Z buffer.
-> in order to only "color" the skydome, but not write into the Z buffer
-> you need to look at your "Standard_3" and in the pass(es), add :
depth_write off
->And if it is drawn first, you can also add :
depth_check off
more details in "3.1.2 Passes" in the manual.

Hope it is simplier?

[AshMcConnell]

Hi MadMarx,

Great! The penny has dropped . I understand what you mean now.

1/ Yeah, I've heard this before - I think there may be a way to render the close objects with a low near clipplane (my cockpit really) and then render the rest with a better ratio'd Far / Near.

2/ My skydome texture seems to be for 360 degrees, should i still tile?

3/ Great! Makes sense now - I thought that drawing it close would mean that i wouldnt see my "normal" scene objects, which was wrong of course, because not writing to the depth buffer allows the other objects to be rendered.

My world is actually a different co-ordinate system to ogre's, so i've added an orientation to rotate it: -

Ogre::Quaternion ori, rotz, roty;
rotz.FromAngleAxis(Ogre::Degree(-90), Vector3::UNIT_Z);
roty.FromAngleAxis(Ogre::Degree(90), Vector3::UNIT_Y);
ori = roty * rotz;

_sceneMgr->_setSkyDome(true, "Standard_3",10, 1, 3, RENDER_QUEUE_SKIES_EARLY,ori);

I *think* this should rotate it to Z up. The dome certainly appears in all 360 degrees (which it didn't before i rotated), but the texture seems to be going the wrong direction.

Here is the texture: -



Here is a screenshot: -



Is it simply a case of rotating the texture?

Thanks for your help - a couple of things have clicked for me today

All the best,
Ash

[AshMcConnell]

Should I be using a cubemap with a skydome?

[madmarx]

By the way you need to add :
lighting off
in the pass of your material.

If you want to rotate a texture, you can also do it directly in the texture_unit script.
It is extremely useful because you don't need to recompile to make some tests.
You can also stretch it, make it move & so on from script.

I personnaly use only cubemap. But cubemap texture is more complex to create (needs 6 textures with given angles & so on).
In your case, I would personnaly have created a manualobject halfsphere from code. I don't really see the point of skydome.
Is it the more appropriated for your needs? maybe.

Good luck!

[AshMcConnell]

Thanks again madmarx,

I have just used a dome created and textured in max and moved it around with the camera position, works nicely!

Thanks!
All the best,
Ash

[AshMcConnell]

Hi Folks,

Found a pretty good overview as to why (and how) to render your skybox / dome last: -

http://ati.amd.com/developer/SwedenTech ... Tricks.pdf

I am going to try and do it the vertex shader method, I will report back if anyone is interested.

All the best,
Ash

[AshMcConnell]

Ok here is the shader code: -

Code: Select all

void main_vp(
	float4 position	: POSITION,	
	float2 texCoord0: TEXCOORD0,	

	out float4 oPosition : POSITION,	
	out float2 uv0	 : TEXCOORD0,	

	uniform float4x4 worldViewProj
	)
{
   oPosition = mul(worldViewProj, position);
   oPosition.z = oPosition.w;
   uv0 = texCoord0;
}

void main_fp(	
	float2 texCoord : TEXCOORD0,

	out float4 color : COLOR,

	uniform sampler2D decalMap : TEXUNIT0
  	)
		
{
   color = tex2D(decalMap, texCoord);
}

and the program file: -

Code: Select all

vertex_program SkydomeVP cg
{
	source ashtrack.cg
	entry_point main_vp
	profiles vs_1_1
	
	default_params
	{
		param_named_auto worldViewProj worldviewproj_matrix
	}
}

fragment_program SkydomeFP cg
{
	source ashtrack.cg
	entry_point main_fp
	profiles ps_2_x arbfp1	
}

and the material: -

Code: Select all

material 14-Default
{
	receive_shadows off
	transparency_casts_shadows off
	technique Map#200
	{
		pass Map#201
		{
			ambient 0.698039 0.698039 0.698039 1
			diffuse 0.698039 0.698039 0.698039 1
			specular 0.898039 0.898039 0.898039 1 20
			emissive 0 0 0 1
			scene_blend one zero
			depth_check on
			depth_write off
			depth_func less_equal
			depth_bias 0 0
			alpha_rejection always_pass 0
			cull_hardware clockwise
			cull_software back
			lighting off
			shading gouraud
			polygon_mode solid
			colour_write on
			max_lights 8
			start_light 0
			iteration once 
			vertex_program_ref SkydomeVP
			{
				param_named_auto worldViewProj worldviewproj_matrix
			}
			fragment_program_ref SkydomeFP
			{
			}
			texture_unit Map#202
			{
				texture dusksky.jpg 2d unlimited  
				binding_type fragment
				tex_coord_set 0
				tex_address_mode wrap wrap wrap
				tex_border_colour 0 0 0 1
				filtering trilinear
				max_anisotropy 1
				mipmap_bias 0
				colour_op_ex modulate src_texture src_current
				alpha_op_ex modulate src_texture src_current
				colour_op_multipass_fallback one zero
				env_map off
			}

		}

	}

}

Make sure you remember to turn the depth_check on for the material, or it'll render in front of your "normal" objects.

Also I changed the renderQueueGroup of the entity of the textured mesh I loaded in order that the skies are rendered last. Note I am not using ogre's internal skydome mechanism here, just a textured dome that I move to the camera position each time.

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entity->setRenderQueueGroup(Ogre::RENDER_QUEUE_SKIES_LATE);

I hope this helps some googler

All the best,
Ash