OpenGL shader builder errors on compiling

Question

I'm using OpenGL shader builder v2.2.2 and took sample code from book. For vertex shader

#version 140
uniform float CoolestTemp;
uniform float TempRange;
uniform mat4  MVPMatrix;
in  vec4  mcVertex;
in  float VertexTemp;

out float Temperature;
void main() {

    Temperature = (VertexTemp - CoolestTemp) /  TempRange;
    gl_Position = MVPMatrix * mcVertex;
}

And for fragment shader

#version 140

uniform vec3 CoolestColor;
uniform vec3 HottestColor;

in float Temperature;
out vec4 FragmentColor;

void main() 
{    
    vec3 color = mix(CoolestColor, HottestColor, Temperature);
    FragmentColor = vec4(color, 1.0);
}

My problem is to execute this code because version 140 and 320 is not supported. Then I tryed to remove versions, compiler said "Invalid qualifiers 'in' in global variable context" and same for 'out', then tried to replace in/out to 'varying' but in fragment shader "Left-hand-side of assignment must not be read-only" error appears. For vertex shader have warning about varying fields will not read in next stages. How can I figure out it to adapt an old-styled code to new? So I'm absolutely new to GLSL

Answer 1

It's much more common to go from the old naming to new. But if you need the other way, the conversion for the vertex shader is:

in --> attribute
out --> varying

For fragment shader:

in --> varying
out --> (delete)

For the out of the fragment shader, you can delete the declaration of the variable. Instead, use the built-in gl_FragColor variable.

For your example, the vertex shader will look like this:

uniform float CoolestTemp;
uniform float TempRange;
uniform mat4  MVPMatrix;
attribute vec4  mcVertex;
attribute float VertexTemp;
varying float Temperature;

void main() {
    Temperature = (VertexTemp - CoolestTemp) /  TempRange;
    gl_Position = MVPMatrix * mcVertex;
}

And the fragment shader:

uniform vec3 CoolestColor;
uniform vec3 HottestColor;
varying float Temperature;

void main() {
    vec3 color = mix(CoolestColor, HottestColor, Temperature);
    gl_FragColor = vec4(color, 1.0);
}