Shading a GeoMipTerrain

General Discussion
1

Hey all,

I am newcomer to Panda 3D but a long time Python and game programmer. My experiences with panda so far have been great :slight_smile:

I do however have a question. I am using a GeoMipTerrain and I am using a pixel shader to do some texture splatting, I then tried to add vertex lighting for an ambient and directional light however I am having no luck. Everything runs however I am not seeing the terrain lit like I would expect from the directional light i.e. it is all the same lighting intensity.

If I turn my shader off and use the built in lighting then everything looks like I would expect (just without texture splatting of course). It appears to me that I am getting incorrect normals from the terrain, I was just wondering whether this can be ruled out as a problem or not?

On a side note I was wondering whether people mainly use lightmaps or realtime lighting for terrains?

Cheers

Aaron

2

The problem is simple: if you have a shader applied, you will need to calculate the shading/lighting in the shader itself.

I use lightmaps myself, but if you need day/night cycles, you’ll probably need realtime lighting.

3

Thanks for the reply :slight_smile:

Yeah I understand that once I write a custom shader that I need to handle lighting calculations myself. That is what I thought I was doing in the shader below as well as doing my texture splatting with 3 textures and the alpha maps packed into the rgb channels of 1 texture.

//Cg
//Cg profile arbvp1 arbfp1

void vshader(in float4 vtx_position : POSITION,
            in float3 vtx_normal : NORMAL,
            in float2 vtx_texcoord0 : TEXCOORD0,
            in uniform float4x4 mat_modelproj,
            in uniform float4x4 trans_model_to_world,
            in uniform float4 k_lightvec,
            in uniform float4 k_lightcolor,
            in uniform float4 k_ambientlight,
            out float l_brightness,
            out float2 l_texcoord0 : TEXCOORD0,
            out float4 l_position : POSITION)
{   
    l_position = mul(mat_modelproj, vtx_position);
    l_texcoord0 = vtx_texcoord0;
  
    // lighting
    float3 N = normalize(vtx_normal);
    float3 L = normalize(k_lightvec.xyz);
    l_brightness = (max(dot(-N, L), 0.0f)* k_lightcolor) + k_ambientlight;
}

void fshader( in float4 l_position : POSITION,
              in float2 l_texcoord0 : TEXCOORD0,
              in float  l_brightness,
              in uniform sampler2D tex_0 : TEXUNIT0,
              in uniform sampler2D tex_1 : TEXUNIT1,
              in uniform sampler2D tex_2 : TEXUNIT2,
              in uniform sampler2D tex_3 : TEXUNIT3,
              out float4 o_color : COLOR )
{
    float4 texelColor0 = tex2D(tex_0, l_texcoord0 * 35.0);
    float4 texelColor1 = tex2D(tex_1, l_texcoord0 * 35.0);
    float4 texelColor2 = tex2D(tex_2, l_texcoord0 * 35.0);
    float4 blendColor = tex2D(tex_3, l_texcoord0);
    o_color = (texelColor0 * blendColor.x) + (texelColor1 * blendColor.y) + (texelColor2 * blendColor.z);
    o_color = texelColor0 * l_brightness;
    o_color.a = 1.0;
}

Provided I supply the correct shader inputs, do you see any reason why this shader is not working for a GeoMipTerrain?

4

Hmm, looks right at first glance. You could try isolating the problem by first checking if the normal is correct (by setting the normal vector as o_color), if that is correct, check k_lightvec, then the dot product by outputting them as color. Then you’ll be able to isolate the problem.

5

great suggestion.

I output the normal vector as a color and it is constant blue for a terrain with a big hill in the middle.
Are the normals supposed to get scaled when you do a terrain_node.setSz()?
If not how could I go about getting correct normals?

I have already tried

terrain_node.setAttrib(RescaleNormalAttrib.make(RescaleNormalAttrib.MRescale))

but that did not seem to help at all

The test shader

//Cg
//Cg profile arbvp1 arbfp1

void vshader(in float4 vtx_position : POSITION,
            in float3 vtx_normal : NORMAL,
            in float2 vtx_texcoord0 : TEXCOORD0,
            in uniform float4x4 mat_modelproj,
            out float3 l_color0: COLOR0,
            out float2 l_texcoord0 : TEXCOORD0,
            out float4 l_position : POSITION)
{   
    l_position = mul(mat_modelproj, vtx_position);
    l_texcoord0 = vtx_texcoord0;
  
    float3 N = normalize(vtx_normal);

    l_color0 = N;
}

void fshader( in float4 l_position : POSITION,
              in float2 l_texcoord0 : TEXCOORD0,
              in float3 l_color0: COLOR0,
              out float4 o_color : COLOR)
{
    o_color.xyz = l_color0;
    o_color.a = 1.0;
}

Cheers

6

Are you using Panda3D 1.6.1? I remember there used to be a bug in the normal calculation in GeoMipTerrain, which I believe was fixed in 1.5.4.

Otherwise can you make a tiny python file for me to test?

7

I am using 1.6.1 and yeah I have read up about the previous problems with terrain normals and I just can’t make sense of what is going on.

I have made a sample app that is extremely simple and sent it to your email address. :slight_smile:

Good luck!

8

All right, here’s the problem. vtx_normal just copies the raw vertex normal from the model - so this is not scaled along with the terrain.
You can fix this by transforming the normals yourself in the shader.

9

Sweet. Thanks for taking the time to help me out.

It feels a lot better knowing for certain what is going on :smiley: