CODEWITHSUNDEEP
opengltransparencytexturesglut
jaiesh
jaiesh

Reputation: 146

Texture Transparency in OpenGL

I am making a texture in my environment that excludes all white pixels. I read in a ppm file and the fourth value is always set to 0 if it is a white pixel. Everything seems to be in order, I have set up my view correctly and so forth. The texture image is visible with my current code, however the image as a whole is not fully opaque. It is highly see through. Is this a problem with how I am setting up my GL_Blend? Why is the entire texture not opaque as it should be only excluding the white pixels?

first three values are read in as rgb values and fourth value is not in file, it is selected depending on the total value of the three previous numbers from rgb. This texture is not loaded every time I render it is in a display list so only done once. 

glPushMatrix();

    FILE *inFile3;
    char dump3[3];
    int max3, k3 = 0;

    inFile3 = fopen("tree.ppm", "r");
    int x3;
    int y3;

    fscanf(inFile3, "%s", dump3);
    fscanf(inFile3, "%d %d", &x3, &y3);


    fscanf(inFile3, "%d", &max3);
    int arraySize3 = y3*(4*x3);
    int pixel3, rgb = 0;
    GLubyte data3[arraySize3];

    for (int i = 0; i < x3; i++) {
        for (int j = 0; j < y3; j++) {
            fscanf(inFile3, "%d", &pixel3);
            data3[k3++] = pixel3;
            rgb += pixel3;

            fscanf(inFile3, "%d", &pixel3);
            data3[k3++] = pixel3;
            rgb += pixel3;

            fscanf(inFile3, "%d", &pixel3);
            data3[k3++] = pixel3;
            rgb += pixel3;

            data3[k3++] = ((rgb) > 760) ? 0 : 255;
            rgb = 0;
        }
    }


    fclose(inFile3);

    glGenTextures(1,&texture3);
    glBindTexture(GL_TEXTURE_2D,texture3);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER,GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,GL_NEAREST_MIPMAP_NEAREST);


    gluBuild2DMipmaps(GL_TEXTURE_2D,4,x3,y3,GL_RGBA,GL_UNSIGNED_BYTE,data3);


    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

    glEnable( GL_TEXTURE_2D );
    glBindTexture( GL_TEXTURE_2D, texture3 );
    glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE );

    glRotatef(180, 0, 0, 0);
    glTranslatef(0, -19, 0);

    glBegin(GL_QUADS);

    glTexCoord2d(0,0); glVertex3f(30,0,10);
    glTexCoord2d(0,1); glVertex3f(30,20,10);
    glTexCoord2d(1,1); glVertex3f(30,20,-10);
    glTexCoord2d(1,0); glVertex3f(30,0,-10);

    glEnd();

    glDisable(GL_TEXTURE_2D);
    glDisable(GL_BLEND);
    glPopMatrix();

Screen shots: Tree is not solid

enter image description here

Upvotes: 0

Views: 1301

Answers (2)

jaiesh
jaiesh

Reputation: 146

In addition to what @bernie pointed out about GluByte arrays and including glBegin/end, the problem was in..

glTexEnvf( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE );

GL_MODULATE needed to be replaced with GL_REPLACE. This fixed the issue. Thanks for your guys' help.

Upvotes: 0

bernie
bernie

Reputation: 10400

If you move the viewpoint really close to the tree, does it become opaque? Or does it if you disable mipmapping?

edit

By moving the eye closer to a tree, the level 0 mipmap (your original image) is used. To select a mipmap, OpenGL computes which level provides the best match between the size of its texels and the size of a pixel.

To disable mipmapping generation, you must use glTexImage2D to upload your texture instead of gluBuild2DMipmaps.

To disable usage of mipmaps, change the following line

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_NEAREST);

to

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

You could also do as Jim Buck suggests and use

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 0);

to force the highest mipmap level used to 0. The lowest being by default 0, this effectively disables mipmapping. By setting GL_TEXTURE_MAX_LEVEL and GL_TEXTURE_BASE_LEVEL to the same value, you will be able to see the content of that specific mipmap level.

All this is to confirm if it's a problem with the mipmaps.

Upvotes: 0

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