Rendering multiple textures at different points on screen without using point sprites

Question

I\'m building an ios drawing app and am having a hard time how to draw paint textures on the screen at different points. Most tutorials online refer to rendering a single te

Answer 1

I finally got this to work. I drew each point where the user touches as a TRIANGLE_STRIP primitive, two of which together result in a square.

    GLfloat *tBuffer = malloc(4 * 2 * sizeof(GLfloat));
    tBuffer[0] = 0.0;
    tBuffer[1] = 1.0;
    tBuffer[2] = 1.0;
    tBuffer[3] = 1.0;
    tBuffer[4] = 0.0;
    tBuffer[5] = 0.0;
    tBuffer[6] = 1.0;
    tBuffer[7] = 0.0;
    glTexCoordPointer(2, GL_FLOAT, 0, tBuffer);

    CGFloat padding = 16;
    vBuffer[0] = xCenter - padding;
    vBuffer[1] = yCenter - padding;

    vBuffer[2] = xCenter + padding;
    vBuffer[3] = yCenter - padding;

    vBuffer[4] = xCenter - padding;
    vBuffer[5] = yCenter + padding;

    vBuffer[6] = xCenter + padding;
    vBuffer[7] = yCenter + padding;

    CGFloat degrees = atan2(end.y - start.y, end.x - start.x) * 180 / M_PI;

    // rotate the texture in the direction of the stroke.
    glMatrixMode(GL_TEXTURE);
    glPushMatrix();
    glTranslatef(0.5, 0.5, 0);
    glRotatef(degrees, 0, 0, 1);
    glTranslatef(-0.5, -0.5, 0);
    glVertexPointer(2, GL_FLOAT, 0, vBuffer);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, count);
    glPopMatrix();
    glMatrixMode(GL_MODELVIEW);

xCenter, yCenter is where the user touches. Padding determines the size of the primitive.

I also rotate the texture, but translate it to the center before rotating since rotation happens with the pivot at the origin otherwise.

Hope this helps!

UPDATE:

I was able to reduce the number of openGL calls by 1 by running the following set of commands for rotation instead:

Note that I was able to reduce the number of OpenGL calls by 1, by running the following set of commands for the rotation (removing push/pop matrix)

    glMatrixMode(GL_TEXTURE);
    glLoadIdentity();
    glTranslatef(0.5, 0.5, 0);
    [GLManager rotateBrush:degrees];
    glTranslatef(-0.5, -0.5, 0);
    [GLManager drawVertexBuffer:vBuffer withVertexNumber:4];
    glMatrixMode(GL_MODELVIEW);`