[1.12.2] How would I rotate an entity radar in the direction the player is looking?

[SapphireSky]

I made a sonar-like entity radar that works fine, but it only faces north.

That wouldn't be a problem if I was making a minimap, but for a radar telling the player which direction they're facing isn't good enough to let the player where exactly these entities are.

I assume rotating it has something to do with comparing the player's look vector against the entity position, but that's an area I've just never been able to understand the math for.

 

The best way I know how would be to check for each of the player's EnumFacing values and subtract or add my i and j variables accordingly, but that still only gives me 4 possible rotations which isn't what I'm trying to do...

 

Can I get any help with this?

 

private void renderRadar()
{
	mc.getTextureManager().bindTexture(res);
	int x = screenwidth - 74;
	int y = 10;

	drawTexturedModalRect(x, y, 192, 188, 64, 68);
	float posx = x + 31.5f;
	float posy = y + 35.5f;
	drawTexturedModalRect(posx, posy, 234, 156, 1, 1);

	int k;
	for (Entity e : entitylist)
	{
		float i = (float) (e.posX - mc.player.posX);
		float j = (float) (e.posZ - mc.player.posZ);
		k = e instanceof EntityMob ? 231
				: e instanceof EntityPlayer ? 234 : e instanceof EntityLiving ? 232 : e instanceof EntityItem ? 233 : 0;
		if (k > 0)
		{
			drawTexturedModalRect(posx + i, posy + j, k, 156, 1, 1);
		}
	}
}

 

[SerpentDagger]

2 hours ago, SapphireSky said:

I made a sonar-like entity radar that works fine, but it only faces north.

What exactly do you mean by this? I'm happy to help where I can, but I need a better idea of what's actually going on, what should be going on, and how the problem exists in between those two states.

(Pictures would be an easy way of demonstrating these things.)

[SapphireSky]

14 hours ago, SerpentDagger said:

What exactly do you mean by this? I'm happy to help where I can, but I need a better idea of what's actually going on, what should be going on, and how the problem exists in between those two states.

(Pictures would be an easy way of demonstrating these things.)

This is what it looks like right now (top-right corner of image).

It only faces north, but I want to rotate the radar so instead of facing north all the time it faces the direction the player is looking.

For example, the player is facing west in the image and as you can see from the radar, the mobs on the screen don't like up.

The second image below is what it should look like if the player is facing this direction, and it should rotate the same way no matter which direction the player is looking.

[SerpentDagger]

Do you want the arrow at the top of the radar to always point upwards (the direction the player is facing), or North?

Regardless, the screen positions of the mobs can be determined in the same way.

 

- Assuming the player's position in the radar is (0, 0), then, without rotation, a mob's position can be (a, b).

- What you want to do is rotate the point around (0, 0) by the amount the player is rotated from North (alpha, in my diagram), which is equal to EntityLivingBase#getRotationYawHead(), plus some number (I think 0 radians). You can take the rectangular (a, b) coordinates of the mob, and turn them into polar (r, theta) coordinates, as shown in the diagram.

- Then, you add the player's alpha to the mob's theta, to get the new mob's theta and the position is rotated.

- Now you just need to turn that position back into rectangular coordinates for the renderer, as shown in the diagram.

 

Edit: Definitely use Math#atan2() for the derivation of theta from (a, b). It'll make your life much easier. Also, all of Math's methods use radians, not degrees. I've included a conversion table in the diagram.

Edited November 22, 2019 by SerpentDagger