Opengl & glsl (vec4 * vec4) redundant

[danielmjc]

Hi, unfortunately I’m not sure this is about glsl. I’m reading Opengl Programming Guide, Ninth Edition.
I’m in trouble with this:

#version 420 core

uniform mat4 model_matrix;
...
layout (location = 0) in vec4 position;
...
void main(void)
{
   vec4 pos = (model_matrix * (position * vec4(1.0, 1.0, 1.0, 1.0)));
   ...
};

So, what’s the point in multiplying “position” times vec4(1.0, 1.0, 1.0, 1.0) ? The result will be “position” with or without vec4(1.0, 1.0, 1.0, 1.0).

Thank you.

[Dark_Photon]

@danielmjc

I’m reading Opengl Programming Guide, Ninth Edition.

   vec4 pos = (model_matrix * (position * vec4(1.0, 1.0, 1.0, 1.0)));

So, what’s the point in multiplying “position” times vec4(1.0, 1.0, 1.0, 1.0) ?

Good point. That looks like some test code someone forgot to remove. Should be a no-op that a good compiler will just discard.

I was going to ask you where in the 9th edition you saw that, but I found it:

• p. 248, Example 5.11: Vertex Shader Used in Geometry Pass of Particle System Simulator