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Opengl: Avoiding Texturing

How to apply a repeating texture that always retains its original scale (1 pixel in the texture = 1 pixel on the screen), regardless of the vertex data with which it is applied.

I understand that this is not the most common task, but is it possible to easily install opengl for this, or do I need to apply some kind of mask to the vertex data that corresponds to its original form?

edit: in my particular case, I am trying to draw two-dimensional ellipses of different sizes with the same pixel pattern. The ellipses are made of a triangular fan, and it's hard for me to draw a repeating texture on it. I was hoping there is some combination of opengl configuration to make this easy. Also, I now understand that it is important to mention that I use opengles for iphone, so GLU is not available.

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3 answers

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OpenGL 2D-:



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const XSize = 640, YSize = 480
glMatrixMode (GL_PROJECTION)
glLoadIdentity ()
glOrtho (0, XSize, YSize, 0, 0, 1)
glMatrixMode (GL_MODELVIEW)
glDisable(GL_DEPTH_TEST)
glClear(GL_COLOR_BUFFER_BIT)

// Now draw with 2i or 2f vertices instead of the normal vertex3f functions.
// And for ES, of course set up your data structures and call drawarrays ofr drawelements.

SwapBuffers()

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http://basic4gl.wikispaces.com/2D+Drawing+in+OpenGL

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http://www.gamedev.net/community/forums/topic.asp?topic_id=96440

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http://www.gamedev.net/community/forums/topic.asp?topic_id=96440
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http://www.zeuscmd.com/tutorials/opengles/17-TextureMapping.php

+6

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#include <GL/glut.h>
#include <cstdlib>
#include <cmath>

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;
}

: ( OpenGL ES 1.1):

#include <GL/glut.h>
#include <cstdlib>
#include <cmath>

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;
}
+2

I'm not sure, but I will try something like this:

Take a model matrix, a perspective matrix, and the like. Drop them together in the correct order by multiplying them. Take this matrix back. Multiply it by your texture matrix (which is probably an identity matrix). Set this as your texture matrix.

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