How to make single color face for a cube in GLSL opegl - opengl

Question

I have a rotating cube which continuously rotates
But it always rendered in such a way with interpolated gradient color
I want to color single face with only one color exactly one triangle piece as below
My GLSL
#version 410 core
attribute vec3 position;
attribute vec3 color;
varying vec3 outColor;
uniform float time;
uniform mat4 matrix;
void main()
{
float theta = time;
float co = cos(theta);
float si = sin(theta);
mat4 rotationY = mat4(co, 0, si, 0,
0, 1, 0, 0,
-si, 0, co, 0,
0, 0, 0, 1);
mat4 rotationX = mat4(1, 0, 0, 0,
0, co, -si, 0,
0, si, co, 0,
0, 0, 0, 1);
outColor = color;
gl_Position = matrix * rotationY * rotationX * vec4(position,1.f);
}
#version 410 core
varying vec3 outColor;
uniform float time;
void main()
{
gl_FragColor = vec4(outColor,1);
}
My GLFW code
glClearColor(1f, 1f, 1f, 1f)
glClear(GL_COLOR_BUFFER_BIT.toUInt() or GL_DEPTH_BUFFER_BIT.toUInt())
var time = glfwGetTime()
glUniform1f!!(uniformTime, time.toFloat())
glDrawElements(GL_TRIANGLES, verticesIndex.size, GL_UNSIGNED_SHORT, NULL)
glfwSwapBuffers(window)
glfwPollEvents()
My color array
[
0.8, 0.007315, 0.026764,
0.01696, 0.8, 0.005661,
0.007843, 0.001524, 0.8,
0.01696, 0.8, 0.005661,
0.007843, 0.001524, 0.8,
0.01696, 0.8, 0.005661,
0.007843, 0.001524, 0.8,
0.01696, 0.8, 0.005661,
0.007843, 0.001524, 0.8,
0.01696, 0.8, 0.005661,
0.007843, 0.001524, 0.8,
0.01696, 0.8, 0.005661
]

Answer 1

The usual way is to create a mesh with color attributes where each face has its own vertices with a color attribute of the same color.
Alternatively, you can try using the flat Interpolation qualifier:
The value will not be interpolated. The value given to the fragment shader is the value from the Provoking Vertex for that primitive.
Vertex shader
#version 410 core
in vec3 position;
in vec3 color;
flat out vec3 outColor;
void main()
{
outColor = color
// [...]
}
Fragment shader:
#version 410 core
flat in vec3 outColor;
out vec4 fragColor;
void main()
{
fragColor = vec4(outColor, 1.0);
}
Another option would be to create an array of colors for each triangle primitive and store this color array in a Shader Storage Buffer Object. Use gl_VertexID to address the color in the vertex shader.
vec4 outColor;
layout(std430, binding = 0) buffer primitiveColors
{
vec4 colors[];
};
void main()
{
outColor = colors[gl_VertexID / 3];
// [...]
}