Rendering a 3D graphic

[kotoko]

Hello all,

I'm developing a shader to render a graphic so I'm trying to make specific heigths (position.y) of specific colors.

I've ran into a problem, the heights go from 0 to 255 and I've devided this into 4 groups of height that are a gradient between different colors. Example: values between 0 and 63.75 have colores between (0, 0, 255) and (0, 255, 255).
I have very abrupt transformations between strips:


The Vertex shader (the part about diffuse color):

float interpolate (float z, float lowerBound, float maxRGB){
    float scaled = z - lowerBound;
    float interval = 63.75;
    return (scaled*maxRGB)/interval;
}
 
void main(){
    //Transformation of the object space coordinate to projection space
    //coordinates.
    //- gl_Position is the standard GLSL variable holding projection space
    //position. It must be filled in the vertex shader
    //- To convert position we multiply the worldViewProjectionMatrix by
    //by the position vector.
    //The multiplication must be done in this order.
    position = g_WorldMatrix * vec4(inPosition, 0.0);
    vec4 pos = vec4(inPosition, 1.0);
    gl_Position = g_WorldViewProjectionMatrix * pos;
    //________________________________________________________________________
    vec4 diffuseColor;
    float i;
    float alpha = 1;
    float interval = 255/4;
    int maxRGB_1 = 1;
    int maxRGB_255 = 255;
    if(position.y < interval){                               // blue to cyan
        i = interpolate (position.y, 0, maxRGB_1);
        diffuseColor = vec4(0, i, maxRGB_255, alpha);
    }
    else if(position.y < interval*2){                        // cyan to yellow
        i = interpolate (position.y, interval*1, maxRGB_1);
        diffuseColor = vec4(i, maxRGB_255, 1-i, alpha);
    }
    else if(position.y < interval*3){                        // yellow to red
        i = interpolate (position.y, interval*2, maxRGB_1);
        diffuseColor = vec4(maxRGB_255, 1-i, 0, alpha);
    }
    else{                                                   // red to dark red
        i = interpolate (position.y, interval*3, 0.5);
        diffuseColor = vec4(1-i, 0, 0, alpha);
    }
    gl_FrontColor = diffuseColor;
    //________________________________________________________________________

In the Fragment Shader I just have:

vec4 diffuseColor = gl_Color;

[Bloodust]

Have you tried moving the vertex shader color calculations to fragment shader ?