opengl: how to avoid texture scaling

Question

How do I apply a repeating texture that always maintains its original scale (1 pixel in the texture = 1 pixel on screen), regardless of the vertex data it is applie

Answer 1

I think the following code snippet is what you're talking about. However, without the hack in reshape() it shimmers pretty badly with GL_NEAREST and non-even viewport sizes. Any insight would be appreciated.

It uses texture coordinate generation though, so I'm not sure what to tell you on the OpenGL ES 1.1 front. A PowerVR rep hinted at a solution, but wasn't very explicit.

#include 
#include 
#include 

static GLuint texName;

void init(void)
{
glClearColor(0,0,0,0);

// create random texture
const int texWidth = 8;
const int texHeight = 8;
GLubyte tex[texHeight][texWidth][4];
for(int i = 0; i < texHeight; i++)
    {
    for(int j = 0; j < texWidth; j++) 
        {
        tex[i][j][0] = (GLubyte) rand()%255;
        tex[i][j][1] = (GLubyte) rand()%255;
        tex[i][j][2] = (GLubyte) rand()%255;
        tex[i][j][3] = (GLubyte) 255;
        }
    }
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

glGenTextures(1, &texName);
glBindTexture(GL_TEXTURE_2D, texName);
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);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, texWidth, texHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, tex);

// planes for texture coordinate generation
GLfloat xp[] = {1,0,0,0};
GLfloat yp[] = {0,1,0,0};
GLfloat zp[] = {0,0,1,0};
GLfloat wp[] = {0,0,0,1};
glTexGeni(GL_S, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);
glTexGeni(GL_T, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);
glTexGeni(GL_R, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);
glTexGeni(GL_Q, GL_TEXTURE_GEN_MODE, GL_EYE_LINEAR);
glTexGenfv(GL_S, GL_EYE_PLANE, xp);
glTexGenfv(GL_T, GL_EYE_PLANE, yp);
glTexGenfv(GL_R, GL_EYE_PLANE, zp);
glTexGenfv(GL_Q, GL_EYE_PLANE, wp);
glEnable(GL_TEXTURE_GEN_S);
glEnable(GL_TEXTURE_GEN_T);
glEnable(GL_TEXTURE_GEN_R);
glEnable(GL_TEXTURE_GEN_Q);

glEnable(GL_DEPTH_TEST);
glShadeModel(GL_SMOOTH);
glEnable(GL_TEXTURE_2D);
glEnable(GL_CULL_FACE);
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
}

void display(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

// projection
glMatrixMode(GL_PROJECTION); glLoadIdentity();
int viewport[4]; glGetIntegerv(GL_VIEWPORT, viewport);
gluPerspective(60.0, (GLdouble)viewport[2]/(GLdouble)viewport[3], 1.0, 100.0 );

// texture matrix trickery
int tw,th;
glMatrixMode(GL_TEXTURE); glLoadIdentity();
glBindTexture(GL_TEXTURE_2D, texName);
glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_WIDTH, &tw);
glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_HEIGHT, &th);
glScaled( (viewport[2]/2)/(GLdouble)tw, (viewport[3]/2)/(GLdouble)th, 0 );
GLdouble proj[16];
glGetDoublev(GL_PROJECTION_MATRIX, proj); // grab projection matrix
glMultMatrixd(proj);

// view transform
glMatrixMode(GL_MODELVIEW); glLoadIdentity();
glTranslatef(0,0,-2.5);

// render textured teapot
glPushMatrix();
const float ANGLE_SPEED = 60; // degrees/sec
float angle = ANGLE_SPEED * (glutGet(GLUT_ELAPSED_TIME) / 1000.0f);
glRotatef(angle*0.5f, 1, 0, 0);
glRotatef(angle, 0, 1, 0);
glRotatef(angle*0.7f, 0, 0, 1);
glScalef(-1,-1,-1); // teapot is wound backwards (GL_CW), so flip it
glutSolidTeapot(1);
glPopMatrix();

glutSwapBuffers();
}

void reshape(int w, int h)
{
// make width/height evenly divisible by 2
w -= (w%2);
h -= (h%2);
glViewport(0, 0, (GLsizei) w, (GLsizei) h);
}

void keyboard (unsigned char key, int x, int y)
{
switch (key) 
    { 
    case 27: exit(0); break;
    default: break; 
    }
}

void idle() { glutPostRedisplay(); }

int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);
glutInitWindowSize(640, 480);
glutInitWindowPosition(100, 100);
glutCreateWindow (argv[0]);
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutKeyboardFunc(keyboard);
glutIdleFunc(idle);

init();
glutMainLoop();
return 0;
}

EDIT: Got the texture matrix only method figured out (should be OpenGL ES 1.1-able):

#include 
#include 
#include 

void glutTexturedCube(GLdouble size)
{
    GLfloat texc[] = {
        1,1,    0,1,    0,0,    1,0,
        0,1,    0,0,    1,0,    1,1,
        1,0,    1,1,    0,1,    0,0,
        1,1,    0,1,    0,0,    1,0,
        0,0,    1,0,    1,1,    0,1,
        0,0,    1,0,    1,1,    0,1,
    };

    GLfloat norm[] = {
        0,0,1,      0,0,1,      0,0,1,      0,0,1,
        1,0,0,      1,0,0,      1,0,0,      1,0,0,
        0,1,0,      0,1,0,      0,1,0,      0,1,0,
        -1,0,0,     -1,0,0,     -1,0,0,     -1,0,0,
        0,-1,0,     0,-1,0,     0,-1,0,     0,-1,0,
        0,0,-1,     0,0,-1,     0,0,-1,     0,0,-1,
    };

    GLfloat vert[] = {
        1,1,1,      -1,1,1,     -1,-1,1,    1,-1,1,
        1,1,1,      1,-1,1,     1,-1,-1,    1,1,-1,
        1,1,1,      1,1,-1,     -1,1,-1,    -1,1,1,
        -1,1,1,     -1,1,-1,    -1,-1,-1,   -1,-1,1,
        -1,-1,-1,   1,-1,-1,    1,-1,1,     -1,-1,1,
        1,-1,-1,    -1,-1,-1,   -1,1,-1,    1,1,-1,
    };

    GLuint idxs[] = { 
        0, 1, 2, 3,     
        4, 5, 6, 7,     
        8, 9, 10, 11,
        12, 13, 14, 15,
        16, 17, 18, 19,
        20, 21, 22, 23,
    };

    glEnableClientState(GL_TEXTURE_COORD_ARRAY);
    glEnableClientState(GL_NORMAL_ARRAY);
    glEnableClientState(GL_VERTEX_ARRAY);
    // feed vertices in as texture coordinates
    glTexCoordPointer(3, GL_FLOAT, 0, vert);
    glNormalPointer(GL_FLOAT, 0, norm);
    glVertexPointer(3, GL_FLOAT, 0, vert);

    glPushMatrix();
    glColor4f(1, 1, 1, 1);
    glScaled(size, size, size);
    glDrawElements(GL_QUADS, sizeof(idxs)/sizeof(idxs[0]), GL_UNSIGNED_INT, idxs);
    glPopMatrix();

    glDisableClientState(GL_TEXTURE_COORD_ARRAY);
    glDisableClientState(GL_NORMAL_ARRAY);
    glDisableClientState(GL_VERTEX_ARRAY);
}

static GLuint texName;

void init(void)
{
glClearColor(0,0,0,0);

// create random texture
const int texWidth = 8;
const int texHeight = 8;
GLubyte tex[texHeight][texWidth][4];
for(int i = 0; i < texHeight; i++)
    {
    for(int j = 0; j < texWidth; j++) 
        {
        tex[i][j][0] = (GLubyte) rand()%255;
        tex[i][j][1] = (GLubyte) rand()%255;
        tex[i][j][2] = (GLubyte) rand()%255;
        tex[i][j][3] = (GLubyte) 255;
        }
    }
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

glGenTextures(1, &texName);
glBindTexture(GL_TEXTURE_2D, texName);
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);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, texWidth, texHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, tex);

glEnable(GL_DEPTH_TEST);
glShadeModel(GL_SMOOTH);
glEnable(GL_TEXTURE_2D);
glEnable(GL_CULL_FACE);
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
}

void display(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

// projection
glMatrixMode(GL_PROJECTION); glLoadIdentity();
int viewport[4]; glGetIntegerv(GL_VIEWPORT, viewport);
gluPerspective(60.0, (GLdouble)viewport[2]/(GLdouble)viewport[3], 1.0, 100.0 );

// view transform
glMatrixMode(GL_MODELVIEW); glLoadIdentity();
glTranslatef(0,0,-3);

// render textured teapot
glPushMatrix();
const float ANGLE_SPEED = 10; // degrees/sec
float angle = ANGLE_SPEED * (glutGet(GLUT_ELAPSED_TIME) / 1000.0f);
glRotatef(angle*0.5f, 1, 0, 0);
glRotatef(angle, 0, 1, 0);
glRotatef(angle*0.7f, 0, 0, 1);

// texture matrix trickery
int tw,th;
glBindTexture(GL_TEXTURE_2D, texName);
glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_WIDTH, &tw);
glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_HEIGHT, &th);
GLint mmode = 0;
glGetIntegerv(GL_MATRIX_MODE, &mmode);
glMatrixMode(GL_TEXTURE); glLoadIdentity();
glScaled( (viewport[2]/2)/(GLdouble)tw, (viewport[3]/2)/(GLdouble)th, 0 );
GLdouble mat[16];
glGetDoublev(GL_PROJECTION_MATRIX, mat);
glMultMatrixd(mat);
glGetDoublev(GL_MODELVIEW_MATRIX, mat);
glMultMatrixd(mat);
glMatrixMode(mmode);

glutTexturedCube(1);
glPopMatrix();

glutSwapBuffers();
}

void reshape(int w, int h)
{
// make width/height evenly divisible by 2
w -= (w%2);
h -= (h%2);
glViewport(0, 0, (GLsizei) w, (GLsizei) h);
}

void keyboard (unsigned char key, int x, int y)
{
switch (key) 
    { 
    case 27: exit(0); break;
    default: break; 
    }
}

void idle() { glutPostRedisplay(); }

int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);
glutInitWindowSize(640, 480);
glutInitWindowPosition(100, 100);
glutCreateWindow (argv[0]);
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutKeyboardFunc(keyboard);
glutIdleFunc(idle);

init();
glutMainLoop();
return 0;
}