Hello, everyone!
I have a problem with my Phong shader... I deleted all the textures, normal maps and specular maps to make a clean test for light in the following scene. There are five spheres in a line (each sphere has exactly the same Z and Y coordinates and a different X coordinate). Above and to the right of the spheres there's a light source. It has the same Z coordinates with the spheres, but it is shifted to the right and upwards. Somehow the light is distributed in a strange fashion, so that the sphere closer to the light source 'reflects' less light towards the viewpoint (camera)...
[attachment=28500:problem.jpg]
From what my eyes are used to seeing, the leftmost sphere should look like the rightmost one, and vice versa. But the actual lit area of the spheres seems to be in reverse relation with the position of the light source. I don't really know how to express that in proper terms.
Can anybody explain this? It does not look intuitive, I think the light is actually reversed somehow, but I cannot understand the reason (must be some direction vector in the shader code or something)...
Here's the basic phong shader I'm using:
#version 300 es
in vec3 position;
in vec3 normal;
in vec2 texcoord;
out vec4 normal0;
out vec4 position0;
uniform mat4 modelMatrix;
uniform mat4 modelViewMatrix;
uniform mat4 modelViewProjectionMatrix;
uniform mat3 normalMatrix;
void main () {
gl_Position = modelViewProjectionMatrix * vec4 (position, 1.);
position0 = modelMatrix * vec4 (position, 1.);
normal0 = modelMatrix * vec4 (normal, 0.);
}
#version 300 es
// fragment properties
in highp vec4 position0;
in highp vec4 normal0;
// camera properties
uniform highp vec3 cameraPosition;
// light properties
uniform highp vec3 lightPosition;
uniform lowp vec4 lightColor;
// material properties
uniform lowp vec4 emissiveColor;
uniform lowp vec4 diffuseColor;
uniform lowp vec4 specularColor;
uniform highp float shininess;
// global ambient light
uniform lowp vec4 ambientColor;
// output
out highp vec4 fragmentColor;
void main () {
// emissive component is as it is
// diffuse component
highp vec4 N = normalize (normal0);
highp vec4 L = normalize (vec4 (lightPosition, 1.) - position0);
fragmentColor = (emissiveColor +
ambientColor +
max (dot (N, L), 0.) * lightColor * diffuseColor +
pow (max (dot (reflect (-L, N), normalize (vec4 (cameraPosition, 1.) - position0)), 0.), shininess) * lightColor * specularColor);
}
