OpenGL Simple Shading, Artifacts

Question

I've been trying to implement a simple light / shading system, a simple Phong lighting system without specular lights to be precise. It basically works, except it has some (in my opinion) nasty artifacts.

My first thought was that maybe this is a problem of the texture mipmaps, but disabling them didn't work. My next best guess would be a shader issue, but I can't seem to find the error.

Has anybody ever experienced a similiar issue or an idea on how to solve this?

Image of the artifacts

Vertex shader:

#version 330 core

// Vertex shader
layout(location = 0) in vec3 vpos;
layout(location = 1) in vec2 vuv;
layout(location = 2) in vec3 vnormal;

out vec2 uv;        // UV coordinates
out vec3 normal;    // Normal in camera space
out vec3 pos;       // Position in camera space
out vec3 light[3];  // Vertex -> light vector in camera space

uniform mat4 mv;    // View * model matrix
uniform mat4 mvp;   // Proj * View * Model matrix
uniform mat3 nm;    // Normal matrix for transforming normals into c-space

void main() {
    // Pass uv coordinates
    uv = vuv;

    // Adjust normals
    normal = nm * vnormal;

    // Calculation of vertex in camera space
    pos = (mv * vec4(vpos, 1.0)).xyz;

    // Vector vertex -> light in camera space
    light[0] = (mv * vec4(0.0,0.3,0.0,1.0)).xyz - pos;
    light[1] = (mv * vec4(-6.0,0.3,0.0,1.0)).xyz - pos;
    light[2] = (mv * vec4(0.0,0.3,4.8,1.0)).xyz - pos;

    // Pass position after projection transformation
    gl_Position = mvp * vec4(vpos, 1.0);
}

Fragment shader:

#version 330 core

// Fragment shader
layout(location = 0) out vec3 color;

in vec2 uv;     // UV coordinates
in vec3 normal;     // Normal in camera space
in vec3 pos;        // Position in camera space
in vec3 light[3];   // Vertex -> light vector in camera space

uniform sampler2D tex;
uniform float flicker;

void main() {
    vec3 n = normalize(normal);

    // Ambient
    color = 0.05 * texture(tex, uv).rgb;

    // Diffuse lights
    for (int i = 0; i < 3; i++) {
        l = normalize(light[i]);
        cos = clamp(dot(n,l), 0.0, 1.0);
        length = length(light[i]);
        color += 0.6 * texture(tex, uv).rgb * cos / pow(length, 2);
    }
}

Almost looks like precision issues. What format are you loading your texture as? — Colonel Thirty Two
It seems independent of the texture. I've just colored the whole room white, but the problem persists. — user3413372

dognotdog dognotdog · Accepted Answer · 2016-02-16T17:58:44

As the first comment says, it looks like your color computation is using insufficient precision. Try using mediump or highp floats.

Additionally, the length = length(light[i]); pow(length,2) expression is quite inefficient, and could also be a source of the observed banding; you should use dot(light[i],light[i]) instead.

OpenGL Simple Shading, Artifacts

2 Answers