Passing a 2d vector as vec4 to a OpenGL ES 2.0 shader

Question

I have a texture position (2d vector), which I multiply by a 4x4 matrix in the shader. Currently I'm passing the vector as a vec2 attribute and then creating a vec4 out of it:

Java :

private static final float[] TEXTURE_COORDINATES = {
        0, 1, // bottom left
        1, 1, // bottom right
        0, 0, // top left
        1, 0, // top right
};

Vertex-shader :

attribute vec2 texturePosition;
uniform mat4 textureMatrix;
// more variables
void main() {
    vec4 tp = vec4(texturePosition.x, texturePosition.y, 1, 1);
    tp = textureMatrix * tp;
    // more code
}

Would it be better (in which way?) to directly pass a vec4 attribute and store the two 1s on the java-side?

Java :

private static final float[] TEXTURE_COORDINATES = {
        0, 1, 1, 1, // bottom left
        1, 1, 1, 1, // bottom right
        0, 0, 1, 1, // top left
        1, 0, 1, 1, // top right
};

Vertex-shader :

attribute vec4 texturePosition;
uniform mat4 textureMatrix;
// more variables
void main() {
    vec4 tp = textureMatrix * tp;
    // more code
}

Answer 1

Would it be better to directly pass a vec4 attribute and store the two 1s on the java-side

No, never send data per vertex if you can just pass it in as constants, it's just a complete waste of bandwidth.

That said if you know ahead of time it's a vec2 input, why on earth are you bothering to use a 4x4 matrix? If all you need it a texture coordinate transform then surely a 2x2 matrix or a 3x3 (for affine) is all you need?

Answer 2

https://en.wikibooks.org/wiki/GLSL_Programming/Vector_and_Matrix_Operations as said there:

"Casting a higher-dimensional vector to a lower-dimensional vector is also achieved with these constructors:"

vec4 a = vec4(-1.0, 2.5, 4.0, 1.0);
vec3 b = vec3(a); // = vec3(-1.0, 2.5, 4.0)
vec2 c = vec2(b); // = vec2(-1.0, 2.5)

"Casting a lower-dimensional vector to a higher-dimensional vector is achieved by supplying these constructors with the correct number of components:"

vec2 a = vec2(0.1, 0.2);
vec3 b = vec3(0.0, a); // = vec3(0.0, 0.1, 0.2)
vec4 c = vec4(b, 1.0); // = vec4(0.0, 0.1, 0.2, 1.0)

or something like this

vec2 position;

gl_Position = gl_ModelViewProjectionMatrix *  vec4(position.x, position.y, 0.0, 1.0);