OpenGL Backgrounds

[Brainer]

Hello.

For my little project, I decided to move back to OpenGL 2.0. The project's a very simple 2D game I'm going to work on with my classmates.

I've got a question regarding rendering backgrounds. I have a 128x128 texture which I want to use as a background. Here's how I do it:

procedure TMainForm.RenderBackground;
var
  Test: TTexture;
  I, J, CellsX, CellsY: Integer;
  Viewport: array[0..3] of GLint;
begin
  Test := TextureLibrary[0];
  I := 0;
  J := 0;

  Test.Bind();
  glPushMatrix();
    glGetIntegerv(GL_VIEWPORT, @Viewport[0]);
    CellsX := (Viewport[2] div Test.TextureWidth) + 1;
    CellsY := (Viewport[3] div Test.TextureHeight) + 1;

    while (True) do
    begin
      glLoadIdentity();
      glTranslatef(I * Test.TextureWidth, J * Test.TextureHeight, 0.0);

      glBegin(GL_QUADS);
        glTexCoord2i(0, Test.TextureHeight);
        glVertex2i(0, 0);
        glTexCoord2i(Test.TextureWidth, Test.TextureHeight);
        glVertex2i(Test.TextureWidth, 0);
        glTexCoord2i(Test.TextureWidth, 0);
        glVertex2i(Test.TextureWidth, Test.TextureHeight);
        glTexCoord2i(0, 0);
        glVertex2i(0, Test.TextureHeight);
      glEnd();

      if (I < CellsX) then
        Inc(I)
      else
      begin
        I := 0;
        Inc(J);
      end;
      if (J >= CellsY) then
        break;
    end;
  glPopMatrix();
  Test.UnBind();
end;

I feel it's not the best way to do the background, so if you could possibly suggest me a better way of doing it, I'd really appreciate it. Note that in the example I use GL_TEXTURE_RECTANGLE_EXT.

[Andru]

First of all you must remove all operations with matrices(glTranslatef and glLoadIdentity) and replace them by shifting X/Y coordinates in glVertx2i. After this you can conclude your "while ( True ) do" like this:

glBegin( GL_QUADS );
while ( True ) do
begin
  // render code without glBegin/glEnd, only glVertex/glTexCoord and some other operations
end;
glEnd;

But only if you use only one 128x128 texture. And one more optimization - do not use glGetIntegerv, try to use constant Width/Height.

[Brainer]

Thanks.
But how do I shift these coordinates?

[Andru]

But how do I shift these coordinates?

Emm...

var
  shiftX, shiftY : Integer;
...
shiftX := I * Test.TextureWidth;
shiftY := J * Test.TextureHeight;
...
  glVertex2i( shiftX, shiftY );
  glTexCoord2i(Test.TextureWidth, Test.TextureHeight);
  glVertex2i(shiftX + Test.TextureWidth, shiftY);
  // and so on :)

[Brainer]

Thanks a lot, Andru!

[User137]

I see that you only use 1 texture which fills the entire texture image. Therefore you can take use of texture clamping with GL_REPEAT. All you need to do is render 1 quad that fills the entire screen and have texture coordinates that multiply themselves as many times as you can fit cells.

from
glTexCoord2f(0,0);
to

(if texture max is 1,1) glTexCoord2f(Form.ClientWidth/Test.TextureWidth, Form.ClientHeight/Test.TextureHeight);
(if texture max is width,height) glTexCoord2f(Form.ClientWidth, Form.ClientHeight);

You can get rid of the whole while loop then... now if i understood the idea correctly.

[Andru]

Therefore you can take use of texture clamping with GL_REPEAT.

How can I forgot about this... Yes, this will be the fastest solution in this case