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OpenGL and transparent square


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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 : width=800 height=449http://www.aht.li/2574678/2015-01-31_021445.png[/img]

And when I move to other face, I have :

width=800 height=449http://www.aht.li/2574679/2015-01-31_021517.png[/img]

width=800 height=449http://www.aht.li/2574680/2015-01-31_021505.png[/img]

width=800 height=449http://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

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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 :/

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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

 

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