CODEWITHSUNDEEP
opengl
gberes
gberes

Reputation: 1169

glTexCoord2d has no effect

I'm trying to draw a simple texture in opengl. I made a simple class Texture:

class Texture{
public:
    unsigned int id;
    unsigned char image[256*256*3];
    int level;
    int border;
    int width;
    int height;    

    Texture (int level =0, int border = 0) : level(level), border(border) {
        glGenTextures(1, &id);
        width = 256, height = 256;
        glTexImage2D(GL_TEXTURE_2D, level, GL_RGB, width, height, border, GL_RGB, GL_UNSIGNED_BYTE, &image[0]);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE); 


        for (int i= 0; i<width*height*3; i+=3){
            image[i]=1;//i%255;
            image[i+1] =1;// 255-i%255;
            image[i+2] =1;// i%128;
        }
    }

    void useIt(){
        glBindTexture( GL_TEXTURE_2D, id );
    }
};

It creates an unsigned char array and fill it with some random data. I'm trying to use it this way:

glEnable(GL_TEXTURE_2D);
texture->useIt();
glBegin(GL_TRIANGLES);

glNormal3d(0, 1, 0);
glTexCoord2d(0.0,0.0);
glVertex3f(width/-2.f,height/2.f,depth/2.f);
glTexCoord2d(1.0,1.0);  
glVertex3f(width/2.f,height/2.f,depth/2.f);
glTexCoord2d(1.0,0.0);
glVertex3f(width/2.f,height/2.f,depth/-2.f);
glTexCoord2d(0.0,0.0);
glVertex3f(width/-2.f,height/2.f,depth/2.f);
glTexCoord2d(1.0,1.0);
glVertex3f(width/2.f,height/2.f,depth/-2.f);
glTexCoord2d(0.0,1.0);
glVertex3f(width/-2.f,height/2.f,depth/-2.f);

glEnd();
glDisable(GL_TEXTURE_2D);

It draws the plane, but withouht texture (draws with the previously used material). what am i doing wrong?

Upvotes: 0

Views: 1669

Answers (2)

datenwolf
datenwolf

Reputation: 162164

Three possible issues with your code. Brett Hale already told you, that you need to bind a texture object before uploading data to it with glTexImage.

glTexImage creates copy of the data you supply to it (this is different to the glVertex…Pointer functions, which only take a pointer or offset into a buffer object). However you're filling the image array with data after you copied it's contents to the texture. Also you may safely delete the image array after copying the data to the texture.

Last but not least: Those operations are found in a constructor. If you have the texture class instance in a scope that's initialized before a OpenGL context has been created, nothing will happen at all, because there's no OpenGL context. So either make sure, the texture object is created only after a OpenGL context is available, or put the texture creation and upload code into a separate method, that you call once a OpenGL context is available.

Upvotes: 1

Brett Hale
Brett Hale

Reputation: 22308

glBindTexture is required in the Texture constructor, prior to the glTex* operations.

You might also require: glPixelStorei(GL_UNPACK_ALIGNMENT, 1) prior to glTexImage2D, since row memory addresses are not on 4-byte boundaries.

BTW..., you need to set the image data before you 'upload' it via glTexImage2D. Right now, you are just setting the texture with uninitialized data. Furthermore, the loop that sets the RGB byte data is just giving you values very close to black, all: (1, 1, 1).

Upvotes: 1

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