l_world_position is just a variable name that the shader uses. It has no meaning with Panda.
If you use a shader, you don’t need projectTexture or gl_TextureMatrix; you can calculate everything in the shader instead of letting Panda do it on the GPU. If you go that route, you do need a special trick to transform the lookup coordinates from (-1, 1) to (0, 1) range. See the Advanced Shadows sample, specifically shadow-nosupport.sha to see how texture projection is done in a Cg shader (shadow mapping is pretty much identical to texture projection except for a comparison check and the fact that a depth texture is projected).
Here’s the code of shadow-nosupport.sha for your convenience:
//Cg
void vshader(float4 vtx_position : POSITION,
float2 vtx_texcoord0: TEXCOORD0,
float3 vtx_normal: NORMAL,
uniform float4x4 trans_model_to_clip_of_light,
uniform float4x4 mat_modelproj,
uniform float4 mspos_light,
uniform float4 k_ambient,
uniform float4 k_scale,
uniform float4 k_push,
out float4 l_position : POSITION,
out float2 l_texcoord0 : TEXCOORD0,
out float4 l_shadowcoord : TEXCOORD1,
out float l_smooth : TEXCOORD2,
out float4 l_lightclip : TEXCOORD3
)
{
float4 position = vtx_position * k_scale;
// vertex position
l_position = mul(mat_modelproj, position);
// Pass through texture coordinate for main texture.
l_texcoord0 = vtx_texcoord0;
// Calculate the surface lighting factor.
l_smooth = saturate(dot(vtx_normal, normalize(mspos_light - position)));
// Calculate light-space clip position.
float4 pushed = position + float4(vtx_normal * k_push, 0);
l_lightclip = mul(trans_model_to_clip_of_light, pushed);
// Calculate shadow-map texture coordinates.
l_shadowcoord = l_lightclip * float4(0.5,0.5,0.5,1.0) + l_lightclip.w * float4(0.5,0.5,0.5,0.0);
}
void fshader(in float2 l_texcoord0 : TEXCOORD0,
in float4 l_shadowcoord : TEXCOORD1,
in float l_smooth : TEXCOORD2,
in float4 l_lightclip : TEXCOORD3,
uniform sampler2D tex_0 : TEXUNIT0,
uniform sampler2D k_Ldepthmap : TEXUNIT1,
uniform float4 k_ambient,
uniform float4 k_texDisable,
out float4 o_color:COLOR)
{
float3 circleoffs = float3(l_lightclip.xy / l_lightclip.w, 0);
float falloff = saturate(1.0 - dot(circleoffs, circleoffs));
float4 baseColor = saturate(tex2D(tex_0, l_texcoord0) + k_texDisable);
float4 proj = l_shadowcoord / l_shadowcoord.w;
float mapval = tex2D(k_Ldepthmap,proj.xy);
float shade = (mapval > proj.z);
o_color = baseColor * ( falloff * shade * l_smooth + k_ambient.x );
}
