Add standard lighting (2/3)

- 3 light types added (point, directional, spot).
- DrawLights() function added using line shapes.
- Standard lighting example added.
- Removed useless struct variables from material and light.
- Fixed light attributes dynamic locations errors.
- Standard vertex and fragment shaders temporally added until rewrite it
as char pointers in rlgl.
TODO:
- Add normal and specular maps calculations in standard shader.
- Add control structs to handle which attributes needs to be calculated
(textures, specular...).
- Adapt standard shader to version 110.
- Rewrite standard shader as char pointers in rlgl.

examples/resources/shaders/standard.fs

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+#version 330
+
+in vec3 fragPosition;
+in vec2 fragTexCoord;
+in vec4 fragColor;
+in vec3 fragNormal;
+
+out vec4 finalColor;
+
+uniform sampler2D texture0;
+
+uniform vec4 colAmbient;
+uniform vec4 colDiffuse;
+uniform vec4 colSpecular;
+uniform float glossiness;
+
+uniform mat4 modelMatrix;
+uniform vec3 viewDir;
+
+struct Light {
+    int enabled;
+    int type;
+    vec3 position;
+    vec3 direction;
+    vec4 diffuse;
+    float intensity;
+    float attenuation;
+    float coneAngle;
+};
+
+const int maxLights = 8;
+uniform int lightsCount;
+uniform Light lights[maxLights];
+
+vec3 CalcPointLight(Light l, vec3 n, vec3 v)
+{
+    vec3 surfacePos = vec3(modelMatrix*vec4(fragPosition, 1));
+    vec3 surfaceToLight = l.position - surfacePos;
+    
+    // Diffuse shading
+    float brightness = clamp(dot(n, surfaceToLight)/(length(surfaceToLight)*length(n)), 0, 1);
+    float diff = 1.0/dot(surfaceToLight/l.attenuation, surfaceToLight/l.attenuation)*brightness*l.intensity;
+    
+    // Specular shading
+    float spec = 0.0;
+    if(diff > 0.0)
+    {
+        vec3 h = normalize(-l.direction + v);
+        spec = pow(dot(n, h), 3 + glossiness);
+    }
+    
+    return (diff*l.diffuse.rgb*colDiffuse.rgb + spec*colSpecular.rgb);
+}
+
+vec3 CalcDirectionalLight(Light l, vec3 n, vec3 v)
+{
+    vec3 lightDir = normalize(-l.direction);
+    
+    // Diffuse shading
+    float diff = clamp(dot(n, lightDir), 0.0, 1.0)*l.intensity;
+    
+    // Specular shading
+    float spec = 0.0;
+    if(diff > 0.0)
+    {
+        vec3 h = normalize(lightDir + v);
+        spec = pow(dot(n, h), 3 + glossiness);
+    }
+    
+    // Combine results
+    return (diff*l.intensity*l.diffuse.rgb*colDiffuse.rgb + spec*colSpecular.rgb);
+}
+
+vec3 CalcSpotLight(Light l, vec3 n, vec3 v)
+{
+    vec3 surfacePos = vec3(modelMatrix*vec4(fragPosition, 1));
+    vec3 lightToSurface = normalize(surfacePos - l.position);
+    vec3 lightDir = normalize(-l.direction);
+    
+    // Diffuse shading
+    float diff = clamp(dot(n, lightDir), 0.0, 1.0)*l.intensity;
+    
+    // Spot attenuation
+    float attenuation = clamp(dot(n, lightToSurface), 0.0, 1.0);
+    attenuation = dot(lightToSurface, -lightDir);
+    float lightToSurfaceAngle = degrees(acos(attenuation));
+    if(lightToSurfaceAngle > l.coneAngle) attenuation = 0.0;
+    float falloff = (l.coneAngle - lightToSurfaceAngle)/l.coneAngle;
+    
+    // Combine diffuse and attenuation
+    float diffAttenuation = diff*attenuation;
+    
+    // Specular shading
+    float spec = 0.0;
+    if(diffAttenuation > 0.0)
+    {
+        vec3 h = normalize(lightDir + v);
+        spec = pow(dot(n, h), 3 + glossiness);
+    }
+    
+    return falloff*(diffAttenuation*l.diffuse.rgb + spec*colSpecular.rgb);
+}
+
+void main()
+{
+    // Calculate fragment normal in screen space
+    mat3 normalMatrix = transpose(inverse(mat3(modelMatrix)));
+    vec3 normal = normalize(normalMatrix*fragNormal);
+   
+    // Normalize normal and view direction vectors
+    vec3 n = normalize(normal);
+    vec3 v = normalize(viewDir);
+
+    // Calculate diffuse texture color fetching
+    vec4 texelColor = texture(texture0, fragTexCoord);
+    vec3 lighting = colAmbient.rgb;
+    
+    for(int i = 0; i < lightsCount; i++)
+    {
+        // Check if light is enabled
+        if(lights[i].enabled == 1)
+        {
+            // Calculate lighting based on light type
+            switch(lights[i].type)
+            {
+                case 0: lighting += CalcPointLight(lights[i], n, v); break;
+                case 1: lighting += CalcDirectionalLight(lights[i], n, v); break;
+                case 2: lighting += CalcSpotLight(lights[i], n, v); break;
+                default: break;
+            }
+        }
+    }
+    
+    // Calculate final fragment color
+    finalColor = vec4(texelColor.rgb*lighting, texelColor.a);
+}

examples/resources/shaders/standard.vs

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+#version 330 
+
+in vec3 vertexPosition;
+in vec3 vertexNormal;
+in vec2 vertexTexCoord;
+in vec4 vertexColor;
+
+out vec3 fragPosition;
+out vec2 fragTexCoord;
+out vec4 fragColor;
+out vec3 fragNormal;
+
+uniform mat4 mvpMatrix;
+
+void main()
+{
+    fragPosition = vertexPosition;
+    fragTexCoord = vertexTexCoord;
+    fragColor = vertexColor;
+    fragNormal = vertexNormal;
+
+    gl_Position = mvpMatrix*vec4(vertexPosition, 1.0);
+}