c++openglvertex-buffer-objectstexture1d

glTexCoordPointer output not as expected


I am trying to use glDrawElements , glTexCoordPointer and glTexImage1D to create a 1D texture, render a surface dataset and color the vertices according to their height value.

GLuint tex = 0;

My texture generation:

glGenTextures( 1, &tex );
glBindTexture( GL_TEXTURE_1D, tex );
unsigned char pixels[] =
{
    255, 0, 0, 255,
    0, 255, 0, 255,
    0, 0, 255, 255,
};
glTexImage1D( GL_TEXTURE_1D, 0, GL_RGBA, 3, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels );
glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL );
glTexParameteri( GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
glTexParameteri( GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
glTexParameteri( GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );

vArray is an array which stores the vertices for rendering.

float vArray[12] = {  
   0.0, 1.0, 0.0,
   0.0, 3.0, 1.0,
   1.0, 2.0, 0.0,
   1.0, 1.0, 1.0,
}

iArray is an array which stores the indices for rendering.

int iSize = 6;
int iArray[6] = {  
   0, 2, 1,
   2, 1, 4,
}

tArray is an array which stores the normalised heights.

GLfloat tArray[4] = {  
   0.0, 0.3, 1.0, 0.0,
}

My render code:

  glEnable(GL_TEXTURE_1D);
  glEnableClientState(GL_TEXTURE_COORD_ARRAY);
  glBindTexture(GL_TEXTURE_1D, tex);
  glTexCoordPointer(1, GL_FLOAT, sizeof(GL_FLOAT), tArray);

  glEnableClientState(GL_VERTEX_ARRAY);
  glVertexPointer(3 ,GL_FLOAT,0, vArray);    

  glDrawElements(GL_TRIANGLES, iSize, GL_UNSIGNED_INT, iArray);

  glDisableClientState(GL_VERTEX_ARRAY);
  glDisableClientState(GL_TEXTURE_COORD_ARRAY);
  glDisable(GL_TEXTURE_1D);

The final output is not as I expected, hoping somebody can point out my mistakes.


Solution

  • All together:

    #include <GL/glew.h>
    #include <GL/glut.h>
    
    GLuint tex = 0;
    void display()
    {
        glClear( GL_COLOR_BUFFER_BIT );
    
        float vArray[] =
        {
           -0.5, -0.5,
            0.5, -0.5,
            0.5,  0.5,
           -0.5,  0.5,
        };
    
        GLfloat tArray[] =
        {
           0.0, 0.3, 1.0, 0.0,
        };
    
        unsigned int iArray[] =
        {
           0, 1, 2,
           2, 3, 0,
        };
    
        glEnable( GL_TEXTURE_1D );
        glBindTexture( GL_TEXTURE_1D, tex );
        glEnableClientState( GL_TEXTURE_COORD_ARRAY );
        glTexCoordPointer( 1, GL_FLOAT, 0, tArray );
    
        glEnableClientState( GL_VERTEX_ARRAY );
        glVertexPointer( 2, GL_FLOAT, 0, vArray );
    
        glDrawElements( GL_TRIANGLES, 6, GL_UNSIGNED_INT, iArray );
    
        glDisableClientState( GL_TEXTURE_COORD_ARRAY );
        glDisableClientState( GL_VERTEX_ARRAY );
        glDisable( GL_TEXTURE_1D );
    
        glutSwapBuffers();
    }
    
    int main( int argc, char** argv )
    {
        glutInit( &argc, argv );
        glutInitDisplayMode( GLUT_RGBA | GLUT_DOUBLE );
        glutInitWindowSize( 400, 400 );
        glutCreateWindow( "GLUT" );
        glewInit();
    
        glGenTextures( 1, &tex );
        glBindTexture( GL_TEXTURE_1D, tex );
        unsigned char pixels[] =
        {
            255, 0, 0, 255,
            0, 255, 0, 255,
            0, 0, 255, 255,
        };
        glTexImage1D( GL_TEXTURE_1D, 0, GL_RGBA, 3, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels );
        glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL );
        glTexParameteri( GL_TEXTURE_1D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
        glTexParameteri( GL_TEXTURE_1D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
        glTexParameteri( GL_TEXTURE_1D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
    
        glutDisplayFunc( display );
        glutMainLoop();
        return 0;
    }
    

    EDIT: 2D version:

    #include <GL/glew.h>
    #include <GL/glut.h>
    
    GLuint tex = 0;
    void display()
    {
        glClear( GL_COLOR_BUFFER_BIT );
    
        float vArray[] =
        {
           -0.5, -0.5,
            0.5, -0.5,
            0.5,  0.5,
           -0.5,  0.5,
        };
    
        GLfloat tArray[] =
        {
           0.0, 0.0,
           1.0, 0.0,
           1.0, 1.0,
           0.0, 1.0,
        };
    
        unsigned int iArray[] =
        {
           0, 1, 2,
           2, 3, 0,
        };
    
        glEnable( GL_TEXTURE_2D );
        glBindTexture( GL_TEXTURE_2D, tex );
        glEnableClientState( GL_TEXTURE_COORD_ARRAY );
        glTexCoordPointer( 2, GL_FLOAT, 0, tArray );
    
        glEnableClientState( GL_VERTEX_ARRAY );
        glVertexPointer( 2, GL_FLOAT, 0, vArray );
    
        glDrawElements( GL_TRIANGLES, 6, GL_UNSIGNED_INT, iArray );
    
        glDisableClientState( GL_TEXTURE_COORD_ARRAY );
        glDisableClientState( GL_VERTEX_ARRAY );
        glDisable( GL_TEXTURE_2D );
    
        glutSwapBuffers();
    }
    
    int main( int argc, char** argv )
    {
        glutInit( &argc, argv );
        glutInitDisplayMode( GLUT_RGBA | GLUT_DOUBLE );
        glutInitWindowSize( 400, 400 );
        glutCreateWindow( "GLUT" );
        glewInit();
    
        glGenTextures( 1, &tex );
        glBindTexture( GL_TEXTURE_2D, tex );
        unsigned char pixels[] =
        {
            255, 0, 0, 255,
            0, 255, 0, 255,
            0, 0, 255, 255,
            0, 0, 255, 255,
        };
        glTexImage2D( GL_TEXTURE_2D, 0, GL_RGBA, 2, 2, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels );
        glTexEnvi( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL );
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
        glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR );
    
        glutDisplayFunc( display );
        glutMainLoop();
        return 0;
    }