Lasers? Lasers.

[weckar]

Hi!

This is honestly more of a personal interest topic than a 'help' topic, although that makes me no less interested in the opinions and answers.

 

To me, one of the most graphically entertaining features of any mod ever are the lasers sent out by Botania's mana spreaders. And lately, now that I've dipped my toe into coding for this game myself, I've found myself wondering how it's done...

 

My immediate assumption would be particles of somekind, but I have never known particles behave so well, or be lag free in such large numbers. I've been playing with particles a bit myself, but for me they actually seem to completely ignore any directional vector I give them...

 

Another way, I suppose, would be tapping directly into the drawing engine. But I also imagine this would be cumbersome, difficult, and not very efficient.

 

So, how would it be (/is it) done? This question just has been tickling my brain for a while now!

[Draco18s]

If it looks like solid beams, then it is most likely done using direct GL calls.  Which aren't that difficult, really.  Its just a matter of knowing the two end points and drawing a line.

 

You'll have to escuse this lump of code, its stolen from my own purposes and some of it is useless to you.  I trimmed what I know is, but there are likely lingering references.

I call this function from a DrawBlockHighlightEvent event, but I am specifically interested in the block the player is looking at.

 

//draw a line between two blocks
private void drawLine(Vec3 blockA, Vec3 blockB) {
	Tessellator tess = Tessellator.instance;
	tess.startDrawing(7);//quads
	tess.setBrightness(15728880);
	tess.setColorOpaque_F(1F, 0F, 0F);//red

	Vec3 recLong = blockA.subtract(blockB);
	Vec3 perpendicular = Vec3.createVectorHelper(recLong.zCoord, recLong.yCoord, -recLong.xCoord);
	perpendicular = perpendicular.normalize();

	float Width = 1f/16f;

	Vec3 R1 = blockA.subtract(blockB);
	Vec3 R2 = blockA.subtract(blockB);
	Vec3 R3 = blockA.subtract(blockB);
	Vec3 R4 = blockA.subtract(blockB);

	R1.xCoord = blockA.xCoord + perpendicular.xCoord * Width;
	R1.zCoord = blockA.zCoord + perpendicular.zCoord * Width;
	R2.xCoord = blockA.xCoord - perpendicular.xCoord * Width;
	R2.zCoord = blockA.zCoord - perpendicular.zCoord * Width;
	R1.yCoord = blockA.yCoord - 0.01;
	R2.yCoord = blockA.yCoord - 0.01;

	R3.xCoord = blockB.xCoord + perpendicular.xCoord * Width;
	R3.zCoord = blockB.zCoord + perpendicular.zCoord * Width;
	R4.xCoord = blockB.xCoord - perpendicular.xCoord * Width;
	R4.zCoord = blockB.zCoord - perpendicular.zCoord * Width;
	R3.yCoord = blockB.yCoord + 0.75;
	R4.yCoord = blockB.yCoord + 0.75;
	tess.addVertex(R1.xCoord + 0.5, R1.yCoord, R1.zCoord + 0.5);
	tess.addVertex(R3.xCoord + 0.5, R3.yCoord, R3.zCoord + 0.5);
	tess.addVertex(R4.xCoord + 0.5, R4.yCoord, R4.zCoord + 0.5);
	tess.addVertex(R2.xCoord + 0.5, R2.yCoord, R2.zCoord + 0.5);

	tess.draw();
}

[weckar]

I have to say I am not familiar with the Vec3 data type, but it looks reasonably straightforward as a coordinate storage.

It does strike me that you are creating 4 vertexes to draw a line, and yet nowhere do you tell the tesselator that is is a line you want to draw. Seems to me that it would prefer to draw a plane somehow?

 

I could definitely see this being a very good first solution, so Kudos (I honestly don't see what your signature talks about!). The laser I'm referring to does seem to be made of... pellets, if there'd be no other word to describe it. As said, it LOOKS like particles, but it seems much to controlled to actually be so - while there are too many of them for them to reasonably be actual entities...

 

Still, this gives me some grounds for trying things out

[Draco18s]

I have to say I am not familiar with the Vec3 data type, but it looks reasonably straightforward as a coordinate storage.

It does strike me that you are creating 4 vertexes to draw a line, and yet nowhere do you tell the tesselator that is is a line you want to draw. Seems to me that it would prefer to draw a plane somehow?

 

tess.addVertex(...);

 

The tessellator (and thereby GL) is in quad drawing mode.  So it expects a multiple of four vertices arranged clockwise around the surface normal.

I chose quads because while there is a line mode (two verts) you don't have control over the thickness of that line.  It would be 1 pixel thick, always.

 

 

 

Probably particles then.  And particles are like ultra-cheap entities.

See this class[/i].

[weckar]

Hmmmm going back to the script you posted above, I realize I have no idea where to actually CALL that from!

 

My first instinct was to use a Block's custom rendering class, but within the method renderWorldBlock I get the exception that it's already Tesselating. Haven't found a way around that, so I continued trying.

 

I figured, maybe on the clientside tick of a BlockEntity. No Exceptions - but no line either...

[Draco18s]

If its already tessellating, then drop the "start" and "end" bits. Magic.

[weckar]

Magic it would be... if not that when I drop those it suddenly says it ISN'T tesselating! What do you want from me, Tesselator!?

[Draco18s]

Show your code.