我有两种纹理。一个是jpg，一个是PNG。我已经渲染了一个立方体，我想使用jpg图像作为背景在立方体的每一个面，然后在这个背景上有png。我尝试了mix()，但我可以通过png看到背景，我不希望这样。有没有什么功能可以为我做到这一点？

片段着色器：

#version 330 core

struct Light {
    vec3 direction;
    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
};

struct Material {
    float shininess;
};

out vec4 FragColor;

in vec3 FragPos;
in vec3 Normal;
in vec2 TexCoords;

uniform vec3 viewPos;
uniform sampler2D texture1;
uniform sampler2D texture2;
uniform Light light;
uniform Material material;

void main() {
    
    // ambient
    vec3 ambient = light.ambient * mix(texture(texture1, TexCoords), texture(texture2, TexCoords), 0.0).rgb;

    // diffuse 
    vec3 norm = normalize(Normal);
    vec3 lightDir = normalize(-light.direction);  
    float diff = max(dot(norm, lightDir), 0.0);
    vec3 diffuse = light.diffuse * diff * mix(texture(texture1, TexCoords), texture(texture2, TexCoords), 0.0).rgb;  

    // specular
    vec3 viewDir = normalize(viewPos - FragPos);
    vec3 reflectDir = reflect(-lightDir, norm);  
    float spec = pow(max(dot(viewDir, reflectDir), 0.0), material.shininess);
    vec3 specular = light.specular * spec * mix(texture(texture1, TexCoords), texture(texture2, TexCoords), 0.0).rgb;  
        
    vec3 result = ambient + diffuse + specular;
    FragColor = vec4(result, 1.0);

}

texture1是png，texture2是JPG。