OpenGL Phong着色

Question

我想渲染对象以查看框内部。

我使用了Phong Shading。

当我使用glPolygonMode(GL_FRONT_AND_BACK, GL_LINE)绘制对象时，图像如下所示：

但是当我使用glPolygonMode(GL_FRONT_AND_BACK, GL_FILL)时，图像看起来像这样：

我想只遮挡矩形部分。所以我想看看盒子里面的物体。这是片段代码，我认为它运作良好。但我不知道为什么我看不到内心。

#version 400

struct LIGHT {
    vec4 position; // assume point or direction in EC in this example shader
    vec4 ambient_color, diffuse_color, specular_color;
    vec4 light_attenuation_factors; // compute this effect only if .w != 0.0f
    vec3 spot_direction;
    float spot_exponent;
    float spot_cutoff_angle;
    bool light_on;
};

struct MATERIAL {
    vec4 ambient_color;
    vec4 diffuse_color;
    vec4 specular_color;
    vec4 emissive_color;
    float specular_exponent;
};

uniform vec4 u_global_ambient_color;
#define NUMBER_OF_LIGHTS_SUPPORTED 4
uniform LIGHT u_light[NUMBER_OF_LIGHTS_SUPPORTED];
uniform MATERIAL u_material;

const float zero_f = 0.0f;
const float one_f = 1.0f;

in vec3 v_position_EC;
in vec3 v_normal_EC;
layout (location = 0) out vec4 final_color;

vec4 lighting_equation(in vec3 P_EC, in vec3 N_EC) {
    vec4 color_sum;
    float local_scale_factor, tmp_float; 
    vec3 L_EC;

    color_sum = u_material.emissive_color + u_global_ambient_color * u_material.ambient_color;

    for (int i = 0; i < NUMBER_OF_LIGHTS_SUPPORTED; i++) {
        if (!u_light[i].light_on) continue;

        local_scale_factor = one_f;
        if (u_light[i].position.w != zero_f) { // point light source
            L_EC = u_light[i].position.xyz - P_EC.xyz;

            if (u_light[i].light_attenuation_factors.w  != zero_f) {
                vec4 tmp_vec4;

                tmp_vec4.x = one_f;
                tmp_vec4.z = dot(L_EC, L_EC);
                tmp_vec4.y = sqrt(tmp_vec4.z);
                tmp_vec4.w = zero_f;
                local_scale_factor = one_f/dot(tmp_vec4, u_light[i].light_attenuation_factors);
            }

            L_EC = normalize(L_EC);

            if (u_light[i].spot_cutoff_angle < 180.0f) { // [0.0f, 90.0f] or 180.0f
                float spot_cutoff_angle = clamp(u_light[i].spot_cutoff_angle, zero_f, 90.0f);
                vec3 spot_dir = normalize(u_light[i].spot_direction);

                tmp_float = dot(-L_EC, spot_dir);
                if (tmp_float >= cos(radians(spot_cutoff_angle))) {
                    tmp_float = pow(tmp_float, u_light[i].spot_exponent);
                }
                else 
                    tmp_float = zero_f;
                local_scale_factor *= tmp_float;
            }
        }
        else {  // directional light source
            L_EC = normalize(u_light[i].position.xyz);
        }   

        if (local_scale_factor > zero_f) {              
            vec4 local_color_sum = u_light[i].ambient_color * u_material.ambient_color;

            tmp_float = dot(N_EC, L_EC);
            if (tmp_float > zero_f) {
                local_color_sum += u_light[i].diffuse_color*u_material.diffuse_color*tmp_float;

                vec3 H_EC = normalize(L_EC - normalize(P_EC));
                tmp_float = dot(N_EC, H_EC); 
                if (tmp_float > zero_f) {
                    local_color_sum += u_light[i].specular_color
                                           *u_material.specular_color*pow(tmp_float, u_material.specular_exponent);
                }
            }
            color_sum += local_scale_factor*local_color_sum;
        }
    }
    return color_sum;
}

void main(void) {  

   final_color = lighting_equation(v_position_EC, normalize(v_normal_EC)); // for normal rendering
}