Add better shader for dirt

data/shaders/sp_advanced_terrain.frag

@@ -0,0 +1,59 @@
+in vec3 bitangent;
+in vec4 color;
+in float hue_change;
+in vec3 normal;
+in vec3 tangent;
+in vec2 uv;
+in float camdist;
+in vec4 world_position;
+in vec3 world_normal;
+
+layout(location = 0) out vec4 o_diffuse_color;
+layout(location = 1) out vec4 o_normal_color;
+
+#stk_include "utils/encode_normal.frag"
+#stk_include "utils/rgb_conversion.frag"
+#stk_include "utils/sp_texture_sampling.frag"
+
+float overlay(float bg, float fg)
+{
+    return bg < 0.5 ? (2.0 * bg * fg) : (1.0 - 2.0 * (1.0 - bg) * (1.0 - fg));
+}
+
+void main()
+{
+    vec4 col = multi_sampleTextureLayer0(uv, camdist);
+    vec4 rock = multi_sampleTextureLayer4(uv, camdist);
+    
+    vec2 uuv = vec2(world_position.x, world_position.z);
+
+
+    float mask_2 = multi_sampleTextureLayer5(uv, camdist).r;
+    mask_2 = pow(mask_2, 1.5);
+
+    float up_mask = dot(vec3(0., 1., 0.), world_normal);
+    up_mask = pow(up_mask + (up_mask * 0.1), 2);
+    up_mask = clamp(up_mask, 0.0, 1.0);
+    //vec3 final_color = mix(col.rgb, rock.rgb, overlay(color.r,  mask_2));
+    vec3 final_color = mix(rock.rgb, col.rgb, overlay(up_mask,  mask_2));
+    //vec3 final_color = mix(vec3(1.0, 0.0, 0.0), vec3(0.0, 1.0, 0.0), overlay(color.r,  mask_2));
+
+#if defined(Advanced_Lighting_Enabled)
+    vec4 layer_2 = multi_sampleTextureLayer2(uv, camdist);
+    vec4 layer_3 = multi_sampleTextureLayer3(uv, camdist);
+    o_diffuse_color = vec4(final_color, layer_2.z);
+
+    vec3 tangent_space_normal = 2.0 * layer_3.xyz - 1.0;
+    vec3 frag_tangent = normalize(tangent);
+    vec3 frag_bitangent = normalize(bitangent);
+    vec3 frag_normal = normalize(normal);
+    mat3 t_b_n = mat3(frag_tangent, frag_bitangent, frag_normal);
+
+    vec3 world_normal = t_b_n * tangent_space_normal;
+
+    o_normal_color.xy = 0.5 * EncodeNormal(normalize(world_normal)) + 0.5;
+    o_normal_color.zw = layer_2.xy;
+#else
+    o_diffuse_color = vec4(final_color, 1.0);
+#endif
+}

data/shaders/sp_kart_dirt.frag

@@ -49,6 +49,7 @@ void main()
     dirtMask *= clamp(dirt_factor, 0.0, 1.0);
     nitroMask *= clamp(dirt_factor, 0.0, 1.0);
     vec3 final_color = col.xyz * color.xyz;
+    //dirtMask = step(dirtMask,dirt_factor - 0.5);
     final_color = mix(final_color, dirt, dirtMask);
 
     final_color = mix(final_color, vec3(0, 0.415, 0.639), nitroMask); 

data/shaders/sps_13_advancedTerrain.xml

@@ -0,0 +1,13 @@
+<spshader>
+    <shader-info name="advancedTerrain" fallback-shader="solid" use-tangents="Y" srgb="Y Y N N Y N"/>
+    <first-pass vertex-shader="sp_pass.vert"
+        fragment-shader="sp_advanced_terrain.frag">
+    </first-pass>
+    <shadow-pass vertex-shader="sp_shadow.vert"
+        fragment-shader="white.frag">
+    </shadow-pass>
+    <uniform-assigners>
+        <uniform-assigner name="layer"
+        function="shadowCascadeUniformAssigner"/>
+    </uniform-assigners>
+</spshader>

src/graphics/skid_marks.cpp

@@ -46,8 +46,8 @@ SkidMarks::SkidMarks(const AbstractKart& kart, float width) : m_kart(kart)
 {
     m_width = width;
     m_material = material_manager->getMaterialSPM("skidmarks.png", "",
-        "alphablend");
+        "alphatest");
-    m_shader = SP::SPShaderManager::get()->getSPShader("alphablend");
+    m_shader = SP::SPShaderManager::get()->getSPShader("alphatest");
     assert(m_shader);
     auto texture = SP::SPTextureManager::get()->getTexture(
         m_material->getSamplerPath(0), m_material,