I am working on a C++ program which displays a terrain mesh using GLSL shaders. I want it to be able to use different materials based on the elevation.
I am trying to accomplish this by having an uniform array of materials in the fragment shader and then using the y coordinate of the world-space position of the current fragment to determine which material from the array to use.
Here are the relevant parts of my fragment shader:
#version 430
struct Material
{
vec3 ambient;
vec3 diffuse;
vec3 specular;
int shininess;
sampler2D diffuseTex;
bool hasDiffuseTex;
float maxY; //the upper bound of this material's layer in relation to the height of the mesh (in the range 0-1)
};
in vec2 TexCoords;
in vec3 WorldPos;
const int MAX_MATERIALS = 14;
uniform Material materials[MAX_MATERIALS];
uniform int materialCount; //the actual number of materials in the array
uniform float minY; //the minimum world-space y-coordinate in the mesh
uniform float maxY; //the maximum world-space y-coordinate in the mesh
out vec4 fragColor;
void main()
{
//calculate the y-position of this fragment in relation to the height of the mesh (in the range 0-1)
float y = (WorldPos.y - minY) / (maxY - minY);
//calculate the index into the materials array
int index = 0;
for (int i = 0; i < materialCount; ++i)
{
index += int(y > materials[i].maxY);
}
//calculate the ambient color
vec3 ambient = ...
//calculate the diffuse color
vec3 diffuse = ...
//sample from the texture
vec3 texColor = vec3(texture(materials[index].diffuseTex, TexCoords.xy));
//only multiply diffuse color with texture color if the material has a texture
diffuse += int(materials[index].hasDiffuseTex) * ((texColor * diffuse) - diffuse);
//calculate the specular color
vec3 specular = ...
fragColor = vec4(ambient + diffuse + specular, 1.0f);
}
It works fine if textures are not used:
But if one of the materials has a texture associated with it, it shows some black artifacts near the borders of the material layer which has the texture:
When I add this line after the diffuse calculation part:
if (index == 0 && int(materials[index].hasDiffuseTex) == 1 && texColor == vec3(0, 0, 0)) diffuse = vec3(1, 0, 0);
it draws the artifacts in red:
which tells me that the index is correct (0) but nothing is sampled from the texture.
Furthermore if I hardcode the index into the shader like this:
vec3 texColor = vec3(texture(materials[0].diffuseTex, TexCoords.xy));
it renders correctly. So I am guessing it has something to do with the indexing but the index appears to be correct and the texture is there so why doesn't it sample color?
I have also found out that if I switch the order of the materials and move their borders around in the GUI of my program in a certain fashion it starts to render correctly from that point on which I don't understand at all. I first suspected that this might be due to me sending wrong values of uniforms to the shaders initially and then somehow it gets the correct ones after I make the changes in the GUI but then I have tested all the uniform values I am sending to the shader from the C++ side and they all appear to be correct from the start and I don't see any other possible problem which might cause this from the C++ side. So I am now thinking the problem is probably in the shader.
