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ursus

OpenGL 2D texture modification in OGL

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Hello, I've been looking around but I'm not quite sure. In my next project apart from 3d world I wish to have 2d ortho things displayed as well. I need to modify 2d textures (like rotating, rescaling, adjusting colors etc). I know I can do it with windows API or external library like SDL but I was wondering if OpenGL supports such things. If so are there some tutorials or articles available? Thanks in advance

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I recall I have found a OGL API to rescale a image to a given size, but was forgotten, Sorry...
The OpenGL Reference Manual (The blue book) version 1.0: OpenGL command specifications:
http://www.rush3d.com/reference/opengl-bluebook-1.0/
I can't find it right now, maybe you can find it.

I don't know there is a OGL API to modify data in texture.
I think you just can do it externally, then send it to make a texture.

Good luck!

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Quote:
Original post by ursus
I need to modify 2d textures (like rotating, rescaling, adjusting colors etc).


Rotation and scaling can be done by mapping a texture to a quad and then rotating/scaling that.
Colour adjustments could be a bit more tricky dependind on what you want to do, unless you target hardware has fragment shaders, in which case its pretty easy [smile]

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For "physical" manipulations of the image such as scale, rotation, translation, skew, etc. you can use the texture matrix to manipulate the texture coords. Just pass GL_TEXTURE in when you set the matrix mode to access the texture matrix.

Color manipulation is a little more tricky. Back in OGL 1.2 there was something called the imaging subset which was an optional part of the OGL spec. This included functionality for manipulating colors, but was optional and not widely implemented.

The color matrix extension was part of this subset and allows color manipulation in rgba space. Support for it seems to be common on ATI hardware but is spotty on other hardware. Your best bet is to do this kind of thing in a fragment shader.

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Quote:
Original post by phantom
Quote:
Original post by ursus
I need to modify 2d textures (like rotating, rescaling, adjusting colors etc).


Rotation and scaling can be done by mapping a texture to a quad and then rotating/scaling that.
Colour adjustments could be a bit more tricky dependind on what you want to do, unless you target hardware has fragment shaders, in which case its pretty easy [smile]

Yes, but if you want to modify data in texture object I think you should recreate it. I don't know OGL can lock texture and modify it's data as in D3D.

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Thank you all very much for your help. I'm new in OGL and was hoping for some easy walk around the problem.

The idea presented by phantom of mapping a texture to some quad and the modify the quad sounds interesting to me. I'm not quite sure how to implement it in 2D though. Some quick example would be greatly appreciated.

What I wish to achieve is a pointer rotation as in speed meter or altitude instrument in planes etc. Besides, sometimes i can see those blown effects with text strings being rescaled, rotated, having pulsing colors etc. and they are drawn basing on bitmap fonts.

I was wondering if it's possible to do it under OGL at all.

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Quote:
Original post by ursus
The idea presented by phantom of mapping a texture to some quad and the modify the quad sounds interesting to me. I'm not quite sure how to implement it in 2D though. Some quick example would be greatly appreciated.

I just change the code by was2_0 :
http://www.gamedev.net/community/forums/topic.asp?topic_id=396992
to make it workable.

#include <windows.h>
#include <gl/gl.h>
#include <gl/glu.h>

int w, h;

unsigned long image[16] = {
0xFF0000FF, 0xFFFF00FF, 0xFF00FFFF, 0xFFFFFFFF,
0xFF00FF00, 0xFFFF0000, 0xFF000000, 0xFFFFFF00,
0x770000FF, 0x777700FF, 0x777777FF, 0xFF7777FF,
0xFF7700FF, 0xFF0077FF, 0xFF770000, 0xFF779933,
};
unsigned int texobj[1];

LRESULT CALLBACK WndProc (HWND hWnd, UINT message,
WPARAM wParam, LPARAM lParam);
void EnableOpenGL (HWND hWnd, HDC *hDC, HGLRC *hRC);
void DisableOpenGL (HWND hWnd, HDC hDC, HGLRC hRC);

int WINAPI WinMain (HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPSTR lpCmdLine,
int iCmdShow)
{
WNDCLASS wc;
HWND hWnd;
HDC hDC;
HGLRC hRC;
MSG msg;
BOOL bQuit = FALSE;

/* register window class */
wc.style = CS_OWNDC | CS_HREDRAW | CS_VREDRAW;
wc.lpfnWndProc = WndProc;
wc.cbClsExtra = 0;
wc.cbWndExtra = 0;
wc.hInstance = hInstance;
wc.hIcon = LoadIcon (NULL, IDI_APPLICATION);
wc.hCursor = LoadCursor (NULL, IDC_ARROW);
wc.hbrBackground = (HBRUSH) GetStockObject (BLACK_BRUSH);
wc.lpszMenuName = NULL;
wc.lpszClassName = "GLSample";
RegisterClass (&wc);

/* create main window */
hWnd = CreateWindow (
"GLSample", "OpenGL Sample",
WS_CAPTION | WS_POPUPWINDOW | WS_VISIBLE | WS_OVERLAPPEDWINDOW,
50, 50, 256, 256,
NULL, NULL, hInstance, NULL);

/* enable OpenGL for the window */
EnableOpenGL (hWnd, &hDC, &hRC);
glEnable(GL_BLEND);
glEnable(GL_TEXTURE_2D);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glGenTextures(1, texobj);
glBindTexture(GL_TEXTURE_2D, texobj[0]);
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, 4, 4, 0, GL_RGBA, GL_UNSIGNED_BYTE, image);

glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, w, h, 0, -1, 1);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
/* program main loop */
while (!bQuit)
{
/* check for messages */
if (PeekMessage (&msg, NULL, 0, 0, PM_REMOVE))
{
/* handle or dispatch messages */
if (msg.message == WM_QUIT)
{
bQuit = TRUE;
}
else
{
TranslateMessage (&msg);
DispatchMessage (&msg);
}
}
else
{
/* OpenGL animation code goes here */

glClearColor (0.0f, 0.0f, 0.0f, 0.0f);
glClear (GL_COLOR_BUFFER_BIT);

glBegin (GL_QUADS);
glTexCoord2f(0.0, 0.0);glColor4f(1.0f, 1.0f, 1.0f, 1.0f);glVertex2f(0.0f, 0.0f);
glTexCoord2f(1.0, 0.0);glColor4f(1.0f, 1.0f, 1.0f, 1.0f);glVertex2f(55.5f, 0.0f);
glTexCoord2f(1.0, 1.0);glColor4f(1.0f, 1.0f, 1.0f, 1.0f);glVertex2f(55.5f, 55.5f);
glTexCoord2f(0.0, 1.0);glColor4f(1.0f, 1.0f, 1.0f, 1.0f);glVertex2f(0.0f, 55.5f);
glEnd ();

SwapBuffers (hDC);

Sleep (1);
}
}

/* shutdown OpenGL */
DisableOpenGL (hWnd, hDC, hRC);

/* destroy the window explicitly */
DestroyWindow (hWnd);

return msg.wParam;
}

LRESULT CALLBACK WndProc (HWND hWnd, UINT message,
WPARAM wParam, LPARAM lParam)
{

switch (message)
{
case WM_SIZE:
w = LOWORD(lParam);
h = HIWORD(lParam);
glViewport(0, 0, LOWORD(lParam), HIWORD(lParam));
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, LOWORD(lParam), HIWORD(lParam), 0, -1, 1);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
return 0;
case WM_CREATE:
return 0;
case WM_CLOSE:
PostQuitMessage (0);
return 0;

case WM_DESTROY:
return 0;

case WM_KEYDOWN:
switch (wParam)
{
case VK_ESCAPE:
PostQuitMessage(0);
return 0;
}
return 0;

default:
return DefWindowProc (hWnd, message, wParam, lParam);
}
}

void EnableOpenGL (HWND hWnd, HDC *hDC, HGLRC *hRC)
{
PIXELFORMATDESCRIPTOR pfd;
int iFormat;

/* get the device context (DC) */
*hDC = GetDC (hWnd);

/* set the pixel format for the DC */
ZeroMemory (&pfd, sizeof (pfd));
pfd.nSize = sizeof (pfd);
pfd.nVersion = 1;
pfd.dwFlags = PFD_DRAW_TO_WINDOW |
PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER;
pfd.iPixelType = PFD_TYPE_RGBA;
pfd.cColorBits = 24;
pfd.cDepthBits = 16;
pfd.iLayerType = PFD_MAIN_PLANE;
iFormat = ChoosePixelFormat (*hDC, &pfd);
SetPixelFormat (*hDC, iFormat, &pfd);

/* create and enable the render context (RC) */
*hRC = wglCreateContext( *hDC );
wglMakeCurrent( *hDC, *hRC );

}

void DisableOpenGL (HWND hWnd, HDC hDC, HGLRC hRC)
{
wglMakeCurrent (NULL, NULL);
wglDeleteContext (hRC);
ReleaseDC (hWnd, hDC);
}



Not quick but somewhat comprehensive.

Quote:
Original post by ursus
What I wish to achieve is a pointer rotation as in speed meter or altitude instrument in planes etc. Besides, sometimes i can see those blown effects with text strings being rescaled, rotated, having pulsing colors etc. and they are drawn basing on bitmap fonts.

I was wondering if it's possible to do it under OGL at all.

I think you may want get a book or tutorial.

Please google by "2D using OpenGL" or others. OpenGL Forum FAQ is another please to go.

Good luck!

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Quote:
Original post by ursus
Thank you all very much for your help. I'm new in OGL and was hoping for some easy walk around the problem.

The idea presented by phantom of mapping a texture to some quad and the modify the quad sounds interesting to me. I'm not quite sure how to implement it in 2D though. Some quick example would be greatly appreciated.

What I wish to achieve is a pointer rotation as in speed meter or altitude instrument in planes etc. Besides, sometimes i can see those blown effects with text strings being rescaled, rotated, having pulsing colors etc. and they are drawn basing on bitmap fonts.

I was wondering if it's possible to do it under OGL at all.


It's very easy to do that under OpenGL. You create a quad, apply a texture to it, then you rotate that quad, scale etc. and in the result, texture also will get scaled, rotated etc.

Rotation is achieved by calling glRotate. Most likely you will have to play with matrices a bit and set other coordinate system.
You create a quad in such a way:

 
glBegin(GL_QUADS);
glVertex2i(10, 10);
glVertex2i(10, 20);
glVertex2i(20, 10);
glVertex2i(20, 20);
glEnd();


To scale, just change those numbers.

You must also call glBindTexture, set texture coordinates etc. And in order to successfully render pictures in 2d, set orthographic projrection (call glOrtho etc.). How to combine it all can be found in any GL tutorial. Also, I recommend to read RedBook.

...

And one more thing. When I'll get your review of "It's horrible! Krzesimir strikes back"?!? ;-)

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