Combining 2d and 3d?

OpenGL OpenGL: Basic Coding
1

Greetings all,

Are you supposed to be able to combine 2d and 3d with OpenGL? For example, the border around the screen in Quake, or the little translator messages that pop up in Unreal?

I can’t get glOrtho and glPerspective to work together - whatever I draw in one gets erased when I switch to the other. If glOrtho isn’t the answer, how can you do this?

Thanks in advance.

2

It works if done correctly, without seeing your code can not point out your error.

Code should look something like this:

void display(void)
{
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); //Clear the screen
// Set perspective view
glMatrixMode (GL_PROJECTION);
glLoadIdentity();
gluPerspective(60, 1, 1, 30);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

Draw_3d();

//Set ortho view
glMatrixMode (GL_PROJECTION); // Tell opengl that we are doing project matrix work
glLoadIdentity(); // Clear the matrix
glOrtho(-9.0, 9.0, -9.0, 9.0, 0.0, 30.0); // Setup an Ortho view
glMatrixMode(GL_MODELVIEW); // Tell opengl that we are doing model matrix work. (drawing)
glLoadIdentity(); // Clear the model matrix

Draw_2d();

}

Originally posted by DalTXColtsFan:
[b]Greetings all,

Are you supposed to be able to combine 2d and 3d with OpenGL? For example, the border around the screen in Quake, or the little translator messages that pop up in Unreal?

I can’t get glOrtho and glPerspective to work together - whatever I draw in one gets erased when I switch to the other. If glOrtho isn’t the answer, how can you do this?

Thanks in advance.[/b]

3

Below is just the render routine, the app is at http://home.att.net/~tennisman5/TryingToCombine.zip.

I can get one or the other, I can switch the order of the 2d and the 3d and get whichever I render 2nd, but I can’t get them both on the screen at the same time.

Any ideas? They will be appreciated.

void Render()
{
// clear screen and depth buffer
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glViewport(0, 0, width, height);	// reset the viewport to new dimensions
	
glMatrixMode(GL_PROJECTION);		// set projection matrix current matrix
glLoadIdentity();					// reset projection matrix
gluPerspective(54.0f,(GLfloat)width/(GLfloat)height,1.0f,1000.0f);

glMatrixMode(GL_MODELVIEW);			// set modelview matrix
glLoadIdentity();					// reset modelview matrix		
		
float angle = rotangle + 90.0f;
if (angle < 0.0f) angle = angle + 360.0f;
if (angle >= 360.0f) angle = angle - 360.0f;
glRotatef(angle, 0.0f, 1.0f, 0.0f);

//Now the translation.  Remember, the camera stays put
//and the world's axes move.  So to simulate moving the
//camera 8 to the right and 8 down, we would move the
//world's axes 8 to the left and 8 up.
float translatex = -personx;
float translatez = -personz;
glTranslatef(translatex, -2.0f, translatez);		// perform transformations

// draw our smooth shaded triangle
glBegin(GL_TRIANGLES);
	glColor3f(1.0f, 0.0f, 0.0f);				// red vertex
	glVertex3f(-1.0f, -1.0f, -.5f);			
	glColor3f(0.0f, 1.0f, 0.0f);				// green vertex
	glVertex3f(2.0f, -1.0f, -.5f);
	glColor3f(0.0f, 0.0f, 1.0f);				// blue vertex
	glVertex3f(-1.0f, 2.0f, -.5f);
glEnd();

myRobot.DrawRobot();

glMatrixMode(GL_PROJECTION);		// set projection matrix current matrix
glLoadIdentity();					// reset projection matrix

glOrtho(0.0f, width - 1.0, 0.0, height - 1.0, -1.0, 1.0);

glMatrixMode(GL_MODELVIEW);			// set modelview matrix
glLoadIdentity();					// reset modelview matrix		

glRasterPos2i(200,200);
glDrawPixels(bitmapData->sizeX, bitmapData->sizeY, GL_RGB, GL_UNSIGNED_BYTE, bitmapData->data);

glFlush();
SwapBuffers(g_HDC);			// bring backbuffer to foreground

}

4

Try extending the depth (far) of your glOrtho call so you can use glRaster3i and set a depth beyond the depth of your other drawings. I just tested it. Works.

I’ve never used glDrawPixels so I’m not sure why, but I had to set the raster pos back nearly as far as the far clip plane. Looking at your code, your objects are only at -50 so I don’t understand it. Perhaps someone else does… or I didn’t look far enough into your code.

Hope it helps.

glOrtho(0.0f, width - 1.0, 0.0, height - 1.0, -1.0, 1000.0);

glMatrixMode(GL_MODELVIEW); // set modelview matrix
glLoadIdentity(); // reset modelview matrix

glRasterPos3i(200,200, -999);
glDrawPixels(bitmapData->sizeX, bitmapData->sizeY, GL_RGB, GL_UNSIGNED_BYTE, bitmapData->data);

glFlush();
SwapBuffers(g_HDC); // bring backbuffer to foreground

5

Thanks shin, I’ll try that when I have a chance. (gotta go back to my DAY JOB right now, woohoo)

So is the generally accepted method for combining 2d and 3d, for doing things like putting a border around the screen like wolf 3d with the player’s health and other data, or displaying messageboxes on the screen like Unreal? If not, what are some other methods that are used in this case?

Thanks

6

Hi,

don’t know if it is useful but there is a demo of using 2D and 3D on HeNe site. He has a 3D rotating box with words around the outside.
It maybe the depth buffer is full up when you swap perspective. Why not try turning depth checking off or clearing the depth buffer before doing your second drawing bit,

fringe

[This message has been edited by fringe (edited 03-18-2003).]

7

I notice you are using drawpixels, you will get some speed increase if you used a texture quad to map you 2D graphics.

Also by using a texture quad you can map transparent areas in your 2D image using the alpha channel, this make you image work more like a overlay image.

On other advantage to a texture quad is on screen re-size, you just stretch the quad to fill the screen vs. on a pixel operation you will have to have extra code to take care of screen size change.