OpenGL and transparent square

[Blackout]

Hi

I try to put a chunk into a box. It's working well when I watch a face but other face doesn't work well. (Sorry for my bad english)

These picture should help you to understand my problem :

 

here it's work : http://www.aht.li/2574678/2015-01-31_021445.png[/img]

And when I move to other face, I have :

http://www.aht.li/2574679/2015-01-31_021517.png[/img]

http://www.aht.li/2574680/2015-01-31_021505.png[/img]

http://www.aht.li/2574681/2015-01-31_021511.png[/img]

 

Here is the code :

​	private void highligthChunk(ForgeFactionChunk c) {


	EntityPlayer player = Minecraft.getMinecraft().thePlayer;

	int xPos = c.xPosition<<4;
	int zPos = c.zPosition<<4;

	drawChunkFaceY(player, xPos, zPos);

	drawChunkFaceX(player, xPos, zPos);
	drawChunkFaceX(player, xPos+16, zPos);

	drawChunkFaceZ(player, xPos, zPos);
	drawChunkFaceZ(player, xPos, zPos+16);
}

private void drawChunkFaceX(EntityPlayer player, int xPos, int zPos) {

	if(player.posX < xPos) {
		GL11.glVertex3f(xPos,player.worldObj.getActualHeight(),zPos);
		GL11.glVertex3f(xPos,0,zPos);
		GL11.glVertex3f(xPos,0,zPos+16);
		GL11.glVertex3f(xPos,player.worldObj.getActualHeight(),zPos+16);
	}else {
		GL11.glVertex3f(xPos,player.worldObj.getActualHeight(),zPos+16);
		GL11.glVertex3f(xPos,0,zPos+16);
		GL11.glVertex3f(xPos,0,zPos);
		GL11.glVertex3f(xPos,player.worldObj.getActualHeight(),zPos);
	}
}

private void drawChunkFaceY(EntityPlayer player, int xPos, int zPos) {
	int y = player.worldObj.getActualHeight();
	if(player.posY < y) {
		GL11.glVertex3f(xPos+16,y,zPos+16);
		GL11.glVertex3f(xPos,y,zPos+16);
		GL11.glVertex3f(xPos,y,zPos);
		GL11.glVertex3f(xPos+16,y,zPos);
	}else {
		GL11.glVertex3f(xPos+16,y,zPos);
		GL11.glVertex3f(xPos,y,zPos);
		GL11.glVertex3f(xPos,y,zPos+16);
		GL11.glVertex3f(xPos+16,y,zPos+16);
	}
}

private void drawChunkFaceZ(EntityPlayer player, int xPos, int zPos) {
	if(player.posZ < zPos) {
		GL11.glVertex3f(xPos+16,player.worldObj.getActualHeight(),zPos);
		GL11.glVertex3f(xPos+16,0,zPos);
		GL11.glVertex3f(xPos,0,zPos);
		GL11.glVertex3f(xPos,player.worldObj.getActualHeight(),zPos);

	}else {
		GL11.glVertex3f(xPos,player.worldObj.getActualHeight(),zPos);
		GL11.glVertex3f(xPos,0,zPos);
		GL11.glVertex3f(xPos+16,0,zPos);
		GL11.glVertex3f(xPos+16,player.worldObj.getActualHeight(),zPos);
	}
}

 

Thanks for your help

[TheGreyGhost]

It is happening because the rendering order of partially transparent objects is important.

 

If you draw the nearest face first, it completely hides the furthest face due to depth culling.

 

You need to draw the further face first, then the nearest face.

 

-TGG

[Blackout]

Thank you for your help TheGreyGhost

I try to sort face by distance, but I don't sucess

Is there a way to do it easy ? In fact, because I use it in a very often called method, I'm scared to write something not enought optimized.

I read that OpenGL Z-Buffer is useless with transparency, I read information about GL_ALPHA_TEST but I don't understand how to use it

[TheGreyGhost]

Hi

 

Unfortunately there is no easier way to do it, but I wouldn't worry about optimising it, if you're only drawing a few faces it will take no time at all even if your code is very inefficient.

 

Because the faces are parallel to the x, y, or z axes, sorting is actually very easy.

 

For example - consider the two faces on the y axis - the top face at y[top] and the bottom face at y[bottom]

Look at the player's y.

If y > y[top], draw the bottom face first

If y < y[bottom], draw the top face first.

Otherwise, it doesn't matter.

 

Similarly with the x and z faces.

 

Once you have figured out which face is furthest for each axis, draw them in this order

x furthest, y furthest, z furthest

then

x closest, y closest, z closest

 

As easy as that

 

You're right that the z buffer will not help you, and GL_ALPHA_TEST is no use to you either.  That's only for textures with pixels that are either fully opaque or fully transparent.

 

-TGG