CODEWITHSUNDEEP
c++opengl-es
Duke
Duke

Reputation: 1731

Rotate Texture2d using rotation matrix

I want to rotate 2d texture in cocos2d-x(opengl es) as i searched i should use rotation matrix as this :

(x = cos(deg) * x - sin(deg) * y y = sin(deg) * x + cos(deg) * y)

but when i want to implement this formula i fail may code is like(i want original x and y to be same ) : i updated my code to this but still not working!

     GLfloat    coordinates[] = {
        0.0f,   text->getMaxS(),
        text->getMaxS(),text->getMaxT(),
        0.0f,   0.0f,
        text->getMaxS(),0.0f };
     glMatrixMode(GL_MODELVIEW);
    glPushMatrix();


    GLfloat vertices[] = {  rect.origin.x,      rect.origin.y,                          1.0f,
                            rect.origin.x + rect.size.width,        rect.origin.y,                          1.0f,
                            rect.origin.x,                          rect.origin.y + rect.size.height,       1.0f,
                            rect.origin.x + rect.size.width,        rect.origin.y + rect.size.height,       1.0f };

    glMultMatrixf(vertices);
    glTranslatef(p1.x, p1.y, 0.0f);
    glRotatef(a,0,0,1);
    glBindTexture(GL_TEXTURE_2D, text->getName());
    glVertexPointer(3, GL_FLOAT, 0, vertices);
    glTexCoordPointer(2, GL_FLOAT, 0, coordinates);
    glColor4f( 0, 0, 250, 1);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
    glRotatef(-a, 0.0f, 0.0f, -1.0f);
    glPopMatrix();

Upvotes: 0

Views: 1415

Answers (2)

Tommy
Tommy

Reputation: 100622

You seem to be confused about a few aspects of OpenGL. At the minute you have this:

glMultMatrixf(vertices);
glTranslatef(p1.x, p1.y, 0.0f);
glRotatef(a,0,0,1);
glBindTexture(GL_TEXTURE_2D, text->getName());
glVertexPointer(3, GL_FLOAT, 0, vertices);
glTexCoordPointer(2, GL_FLOAT, 0, coordinates);
glColor4f( 0, 0, 250, 1);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
glRotatef(-a, 0.0f, 0.0f, -1.0f);
glPopMatrix();

That would ostensibly:

// reinterpret your vertices as a matrix; multiply the
// current matrix by the one formed from your vertices
glMultMatrixf(vertices);

// rotate by a degrees, then translate to p1
glTranslatef(p1.x, p1.y, 0.0f);
glRotatef(a,0,0,1);

// bind the relevant texture, supply the vertices
// as vertices this time, supply texture coordinates
glBindTexture(GL_TEXTURE_2D, text->getName());
glVertexPointer(3, GL_FLOAT, 0, vertices);
glTexCoordPointer(2, GL_FLOAT, 0, coordinates);

// set a colour of (0, 0, 1, 1) — probably you
// wanted glColor4ub to set a colour of (0, 0, 250/255, 1)?
glColor4f( 0, 0, 250, 1);

// draw some geometry
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

// perform the same rotation as before a second time;
// giving either a and -1, or -a and 1 would have been
// the opposite rotation
glRotatef(-a, 0.0f, 0.0f, -1.0f);

// remove the current matrix from the stack
glPopMatrix();

What you probably want is:

// push the current matrix, so that the following
// transformations can be undone with a pop
glPushMatrix();

// rotate by a degrees, then translate to p1
glTranslatef(p1.x, p1.y, 0.0f);
glRotatef(a,0,0,1);

// bind the relevant texture, supply the vertices
// as vertices this time, supply texture coordinates
glBindTexture(GL_TEXTURE_2D, text->getName());
glVertexPointer(3, GL_FLOAT, 0, vertices);
glTexCoordPointer(2, GL_FLOAT, 0, coordinates);

// set a colour of (0, 0, 250/255, 1)
glColor4ub( 0, 0, 250, 1);

// draw some geometry
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

// remove the current matrix from the stack
glPopMatrix();

The current transform matrices are applied to all geometry. You don't flag up which geometry they apply to and which they don't. Pushes and pops should be paired, and are the way you affect transformations from being affected by prior transformations when that's what you want. So you don't manually perform the inverse rotation, and you need to push before you do all the stuff that changes the matrix. I've also switched you to glColor4ub for the reason given above — you appear to be using unsigned bytes to push colours in but OpenGL uses the range from 0.0 to 1.0 to represent a colour. glColor4ub will automatically map from the former to the latter.

Upvotes: 1

Michael Slade
Michael Slade

Reputation: 13877

If you're using OpenGL in two dimensions, you can still use the various transformation functions. For glRotate(), you have to pass it an axis of (0,0,1):

glRotate(angle,0,0,1);

Upvotes: 2

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