Transparent textures being rendered as black in OpenGL

Question

I have a texture with transparent parts, but instead of being rendered transparent they’re black.

To test if the RGBA values get passed on correctly to the shader, I made everything render in greyscale. And as I thought the alpha values weren’t getting passed on correctly.

So anyway here is how the textures get loaded:

    @classmethod
    def load_texture(cls, file_name: str):
        try:
            img = Image.open(f"{sys.path[0]}/res/{file_name}.png").convert('RGBA')
            img = img.transpose(Image.FLIP_TOP_BOTTOM)  # flip image upside down
        except Exception as e:
            print(e)
            img = Image.open(f"{sys.path[0]}/res/missing_texture.png").convert('RGBA')
            img = img.transpose(Image.FLIP_TOP_BOTTOM)  # flip image upside down

        ix, iy, image = img.size[0], img.size[1], img.tobytes("raw", "RGBA", 0, -1)

        texture_id = glGenTextures(1)             # generate a texture ID
        cls.__textures.append(texture_id)
        glBindTexture(GL_TEXTURE_2D, texture_id)  # make it current
        # copy the texture into the current texture texture_id
        glTexImage2D(GL_TEXTURE_2D, 0, 3, ix, iy, 0, GL_RGBA, GL_UNSIGNED_BYTE, image)

        glPixelStorei(GL_UNPACK_ALIGNMENT, 1)
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST)
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST)

        return texture_id

And this is my fragment shader (the commented out part is obviously not working):

#version 400 core

in vec2 pass_texture_coords;
in vec3 surface_normal;
in vec3 to_light_vector;
in vec3 to_camera_vector;

out vec4 out_color;

uniform sampler2D model_texture;
uniform vec3 light_color;
uniform float shine_damper;
uniform float reflectivity;

void main(void){
    vec4 texture_color = texture(model_texture, pass_texture_coords);
    texture_color = vec4(vec3(texture_color.a), 1.0);
    //if(texture_color.a < 0.5){
    //    discard;
    //}

    vec3 unit_normal = normalize(surface_normal);
    vec3 unit_light_vector = normalize(to_light_vector);

    float n_dot1 = dot(unit_normal, unit_light_vector);
    float brightness = max(n_dot1, 0.1);
    vec3 diffuse = brightness * light_color;

    vec3 unit_vector_to_camera = normalize(to_camera_vector);
    vec3 light_direction = -unit_light_vector;
    vec3 reflected_light_direction = reflect(light_direction, unit_normal);

    float specular_factor = dot(reflected_light_direction, unit_vector_to_camera);
    specular_factor = max(specular_factor, 0.0);
    float damped_factor = pow(specular_factor, shine_damper);
    vec3 final_specular = damped_factor * reflectivity * light_color;

    out_color = vec4(diffuse, 1.0) * texture_color + vec4(final_specular, 1.0);
}

Also before rendering anything, this method gets called:

@staticmethod
    def update_display():
        InputController().apply_input()                     # apply inputs every frame

        glEnable(GL_BLEND)
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)   # so that transparent bits of the texture won't get rendered
        glEnable(GL_ALPHA_TEST)

        glEnable(GL_DEPTH_TEST)
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)  # Remove everything from screen (i.e. displays all white)
        glClearColor(0, 0.3, 0, 1)                          # set backdrop color
        glLoadIdentity()                                    # Reset all graphic/shape's position

Asked By: Andreas Sabelfeld

||

Source

Answer 1

From glTexImage2D:

glTexImage2D(
    GL_TEXTURE_2D,    // Target
    0,                // Level
    3,                // Internalformat -> 3 -> GL_RGB -> no alpha
                      // Framebuffer does not necessarily
                      // need an alpha channel.
                      // But if you want transparent textures
                      // you have to specify one,
                      // E.g. GL_RGBA (or any other format
                      // from Table 2 with alpha).
    ix,               // Width
    iy,               // Height
    0,                // Border, must be 0
    GL_RGBA,          // Format of data
    GL_UNSIGNED_BYTE, // Type of data
    image             // Data, which gets converted from format
                      // to internalformat. In your case, the
                      // alpha components will be discarded
);

Hint: always use symbols, e.g., GL_XXXX. Legacy OpenGL accepts a numeric value for internalformat, but the specification in the link above explicitly mandates one of the symbols from the tables.

Answered By: Erdal Küçük

Transparent textures being rendered as black in OpenGL

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