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2d problem

Started by win_crook Aug 13, 2006 at 11:36 AM 8 replies 1.2k views

Original Post

Aug 13, 2006 at 11:36 AM

I am trying to draw a semi-transparent square to my window... Here is the code:


float r = 1, g = 0, b = 0, a = 0.5;
float x = 20, y = 20, xsize = 80, ysize = 80;
window.glEnable2D();
glColor4f(r, g, b, a);
glBegin(GL_QUADS);
glVertex2f(x, y);
glVertex2f(x, y+ysize);
glVertex2f(x+xsize, y+ysize);
glVertex2f(x+xsize, y);
glEnd();
window.glDisable2D();

And here are the enable and disable 2d commands:


void Window::glEnable2D()
{
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluOrtho2D(0, screen->w, screen->h, 0);
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
}

void Window::glDisable2D()
{
	glMatrixMode(GL_PROJECTION);
	glTranslatef(0, -2.0, 0);
	glLoadIdentity();
	gluPerspective(60, 1.33333333, 1, 1024);
}

Excuse the programmer art: Here is a screenshot of what is happening... it is being drawn in the right place but won't go the right colour.

Any ideas to what is wrong? Cheers ~David [Edited by - win_crook on August 13, 2006 11:52:51 AM]

SiCrane

Mod

473

SiCrane

Aug 13, 2006 at 11:40 AM

Did you call glEnable() with GL_BLEND? Did you set an appropriate value with glBlendFunc()?

win_crook

Author

win_crook

Aug 13, 2006 at 11:51 AM

No, I didn't know you had to do that but if you switch it onto glColor3f() and take away the alpha value so it isn't needed it is still the same colour when it should be red.

OrangyTang

335

OrangyTang

Aug 13, 2006 at 11:59 AM

So your vertex colours aren't showing? That usually means you've left lighting enabled and/or you've got an unexpected texture still bound.

win_crook

Author

win_crook

Aug 13, 2006 at 12:42 PM

Thankyou, I forgot to disable lighting. Now how do I make the square translucent with the alpha value.

~David

OrangyTang

335

OrangyTang

Aug 13, 2006 at 12:56 PM

glEnable(GL_BLEND);glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); // For regular transparency

win_crook

Author

win_crook

Aug 13, 2006 at 1:23 PM

thanks again all working now

win_crook

Author

win_crook

Aug 13, 2006 at 2:13 PM

I made a mistake when I said it is all working. The (supposedly)translucents square doesn't blend with textures... e.g:

When the square is over the terrain texture you cannot see the texture through it... the same with the sky. Is there another blend function I need to use or something?

OrangyTang

335

OrangyTang

Aug 13, 2006 at 2:18 PM

Screenshot?

I'm guessing that you're having depth buffer issues. Remember that transparent surfaces must be rendered after all solid surfaces, and generally hud stuff is done in a separate pass drawn last with the depth buffer disabled.

win_crook

Author

win_crook

Aug 13, 2006 at 2:26 PM

Oh ok... I'm new to this transparancy lark, if it doesn't work after I have tried what you have said I'll post another screenshot.

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