simple per vertex shading example

gc-simple.frag.glsl

#version 330

in vec2 uv;
in vec3 diffuse;
in vec3 specular;
in vec2 color_mixes; // x=diffuse mix, y=specular mix

out vec4 outColor;

uniform sampler2D texture0;

void main() {
	vec4 color = texture(texture0, uv);
	vec3 tex_diffuse = diffuse * color_mixes.x;
	vec3 tex_specular = specular * color_mixes.y;
	outColor = vec4(tex_diffuse + tex_specular, color.a);
}

gc-simple.vert.glsl

#version 330

uniform mat4 matVP;  // view/projection matrix
uniform mat4 matGeo; // object matrix
uniform mat4 matInvView; // inverse view matrix

layout (location = 0) in vec3 a_pos;
layout (location = 1) in vec3 a_normal;
layout (location = 2) in vec2 a_uv;
layout (location = 3) in vec4 a_color;

out vec2 uv;
out vec3 diffuse;
out vec3 specular;
out vec2 color_mixes;

struct Material {
	vec4 color;
	float ambient;
	float shininess;
	float diffuse_mix;
	float specular_mix;
};

struct Light {
	vec3 dir;
	vec3 color;
};

void main() {
	uv = a_uv;

	Material mat;
	mat.color = vec4(1.0, 0.5, 1.0, 1.0);
	mat.ambient = 0.5;
	mat.shininess = 5.0;
	mat.diffuse_mix = 1.0;
	mat.specular_mix = 1.0;

	Light light1;
	light1.dir = vec3(0.0, -0.707, -0.707);
	light1.color = vec3(1.0, 1.0, 1.0);

	Light light2;
	light2.dir = vec3(0.0, 0.707, 0.707);
	light2.color = vec3(0.25, 0.1, 0.1);

	color_mixes = vec2(mat.diffuse_mix, mat.specular_mix);
	color_mixes *= exp2(-1.0); // just darken

	diffuse = vec3(mat.ambient);
	diffuse += vec3(max(0.0, dot(light1.dir, a_normal))) * light1.color;
	diffuse += vec3(max(0.0, dot(light2.dir, a_normal))) * light2.color;
	diffuse *= mat.color.rgb * a_color.rgb;

	vec3 view_dir = normalize(mat3(matInvView) * vec3(0.0, 0.0, -1.0));
	specular = vec3(0.0);
	specular += vec3(pow(max(0.0, dot(reflect(-light1.dir, a_normal), view_dir)), mat.shininess)) * light1.color;
	specular += vec3(pow(max(0.0, dot(reflect(-light2.dir, a_normal), view_dir)), mat.shininess)) * light2.color;

	gl_Position = matVP * matGeo * vec4(a_pos, 1.0);
}