I'm working on a user interface system, and I want to be able to mix textured polies with frag-coloured polies. Here's my shader code, that doesn't work:

attribute vec2 vertex_coords;
attribute float texid;
attribute vec4 fragdetails;

varying float usingtex;
varying vec4 v_fragdetails;

void main(){
    gl_Position =  gl_ModelViewProjectionMatrix * vec4(vertex_coords,0.0,1.0);
    
    usingtex = texid;
    v_fragdetails = fragdetails;
}

Fragment:

varying float usingtex;
varying vec4 v_fragdetails;

uniform sampler2D thetexture;

void main() {
    if (usingtex != 0.0){
        thetexture = int(usingtex);
        gl_FragColor = texture2D(thetexture, vec2(v_fragdetails[0], v_fragdetails[1]));
    } else {
        thetexture;
        gl_FragColor = v_fragdetails;
    }
}

Frag_details consists of either [0, r, g, b, a] for a coloured poly, or [texture id, texture x, texture y, 0, 0] for a textured one.

However, samplers must be uniform, and uniforms can't be modified. So how on earth would I swap between textures in one draw? Do I have to set them all up as uniforms and then pick from those? I'd have to use an array, and know the length, which isn't really practical for a UI system where buttons will be clicked, tabs changed, and so on.

Is there a way to do this?

I'm working on a user interface system, and I want to be able to mix textured polies with frag-coloured polies. Here's my shader code, that doesn't work:

attribute vec2 vertex_coords;
attribute float texid;
attribute vec4 fragdetails;

varying float usingtex;
varying vec4 v_fragdetails;

void main(){
    gl_Position =  gl_ModelViewProjectionMatrix * vec4(vertex_coords,0.0,1.0);
    
    usingtex = texid;
    v_fragdetails = fragdetails;
}

Fragment:

varying float usingtex;
varying vec4 v_fragdetails;

uniform sampler2D thetexture;

void main() {
    if (usingtex != 0.0){
        thetexture = int(usingtex);
        gl_FragColor = texture2D(thetexture, vec2(v_fragdetails[0], v_fragdetails[1]));
    } else {
        thetexture;
        gl_FragColor = v_fragdetails;
    }
}

Frag_details consists of either [r, g, b, a] for a coloured poly, with texid set to 0, or [texture x, texture y, 0, 0] for a textured one.

However, samplers must be uniform, and uniforms can't be modified. So how on earth would I swap between textures in one draw? Do I have to set them all up as uniforms and then pick from those? I'd have to use an array, and know the length, which isn't really practical for a UI system where buttons will be clicked, tabs changed, and so on.

Is there a way to do this?