Hello!
I'm trying to reproduce something I did using blender nodes. I have 5 textures, but one of them is a map. I use its RGBA channels as the factors to mix the textures with black and then, finally add them up.

This is my Fragment Shader:
varying vec2 texCoord;

uniform sampler2D textureUnit0;
uniform sampler2D textureUnit1;
uniform sampler2D textureUnit2;
uniform sampler2D textureUnit3;
uniform sampler2D textureUnit4;


const vec3 BLACK = vec3(0.0,0.0,0.0);
const vec3 YELLOW = vec3(0.5,0.5,0.0);

void main (){

vec2 newTexCoords = texCoord * 20.0;

vec4 map = texture2D(textureUnit0, texCoord);
vec4 asphalt = texture2D(textureUnit1, newTexCoords);
vec4 grass = texture2D(textureUnit2, newTexCoords);
vec4 ground = texture2D(textureUnit3, newTexCoords);
vec4 wall = texture2D(textureUnit4, newTexCoords);

vec3 a = mix(BLACK, asphalt.rgb, map.r);
vec3 b = mix(BLACK, grass.rgb, map.g);
vec3 c = mix(BLACK, ground.rgb, map.b);
vec3 d = mix(BLACK, wall.rgb, map.a);

        vec3 result = a+b+c+d;


gl_FragColor = vec4(result,1.0);
}This is the result:
https://drive.google.com/file/d/1DHwsnlmv_Htm43qofuhufOIMA8vHlSWv/view?usp=drive_link

Just by changing the line:
vec3 result = a+b+c+d;to
vec3 result = a+b+c+mix(BLACK, YELLOW, map.a);
I almost got what I want:
https://drive.google.com/file/d/1Bqms-MgMFlo6VSv2Ualm0A6MSS4Qdshn/view?usp=drive_link
But in this case I'm not really using my 4 textures, just 3 and a color created inside the shader.

The problem seems to be in textureUnit4 I think it's not being passed to the shader and thus, it results in a black color, which makes no difference in the final sum. How many textures can I add to a TextureInfo object? If the maximum is 4, then, that must be the reason why my fifth sampler2D uniform is ignored.

p.s. I even wrote this before initalizing my FrameBuffer
Config.maxTextureLayers = 10;but no success, unfortunately.