X_SPRITE MidHandle?

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I'm currently doing a simple 3D particle system for my game and it would be very handy to be able to have the X_SPRITE handle to be centred rather than bottom middle as it is at the moment.

Is there any way to use / have X_SPRITE draw images with the x,y coors referring to the middle of the image rather than the bottom middle?


No there is no easy way to do this at the moment. Also, don't try to play around with alpha if you are using x_sprite, it just doesn't work unless you sort the sprites so you draw the ones further away before you draw the close ones.

I would love a way to set the hotspot on both x_sprite and sprites in 2D so you can rotate around a certain spot, not just the middle. This was very handy in STOS basic on the Atari, can we have it in this nice modern thing too? :-)

Kitty Hello

not really. But it's just the "Y" position that you have to decrease. It's linear to the sprite size and the scaling of the sprite. I "think" the X_Sprite scaling of 1.0 is 100 pixels = 1.0 units in 3D.


Or you can create your own sprite commands, e.g. like this:

Code (glbasic) Select
//! you just have to create one billboard and you can use it with different textures later
// \param num - objectnumber (using X_OBJ...), you need this to draw the billboard later
// \param sz - size of the billboard
FUNCTION CreateBillboard: num, sz
X_OBJADDVERTEX  sz, -sz,  sz, 1, 1, RGB(255,255,255)
X_OBJADDVERTEX -sz, -sz,  sz, 0, 1, RGB(255,255,255)
X_OBJADDVERTEX  sz,  sz,  sz, 1, 0, RGB(255,255,255)
X_OBJADDVERTEX -sz,  sz,  sz, 0, 0, RGB(255,255,255)

//! draw a billboard (stretch and rotate it, if needed) - dont forget to texture it ;)
// \param num - objectnumber created with CreateBillboard()
// \param x,y,z - position (of the center) of the billboard
// \param cx,cy,cz - billboard will point at this (normaly this is the cameraposition)
// \param scale,rotate - make the billboard fit your needs ;)
FUNCTION DrawBillboard: num, x,y,z, cx,cy,cz, scale=1, rotation=0
X_MOVEMENT x, y, z
X_SCALING scale, scale, scale
X_ROTATION rotation, 0,0,1
IF NOT z THEN INC z, 0.0000000000001
X_ROTATION -ATAN((cy-y)*COS(ATAN(cx-x, ABS(z))), ABS(z)), 1,0,0
X_ROTATION ATAN(cx-x, z), 0,1,0
X_DRAWOBJ num, 0

If you optimize this (use qqsin, create triangle instead of quad,...) and make it fit your needs (dont rotate it, if you dont need rotation,..), im sure it can be faster that X_SPRITE and it will do everythink you need.
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kanoent, some great routines there!

I'm not experienced with matrices, but could billboarding be done faster / easier with a matrix?

A quick Google search gave me this: (OpenGL of course, in C)
Code (glbasic) Select
GLfloat matrix[16]; 
matrix[0] = 1.0f;
matrix[1] = 0.0f;
matrix[2] = 0.0f; 
matrix[4] = 0.0f;
matrix[5] = 1.0f;
matrix[6] = 0.0f; 
//render your billboards here   

Or here's a link the goes into full detail about billboarding:
My current project (WIP) :: TwistedMaze <<  [Updated: 2015-11-25]


ive been playing with a 3d particle engine, i named spritez3d...
its not done yet, because of an issue with opengl..z ordering.

heres some stuff you can use...
you can make a particle out of anything...even missles...

This creates a centered billboard
Code (glbasic) Select

FUNCTION EmitterSys_X_CreateSquare: Color
//flat square object, facing +z direction
X_AUTONORMALS 2 // smooth edges
X_OBJADDVERTEX 0.5,0.5,0, 1,0, Color
X_OBJADDVERTEX -0.5,0.5,0, 0,0, Color
X_OBJADDVERTEX -0.5,-0.5,0, 0,1, Color
X_OBJADDVERTEX -0.5,-0.5,0, 0,1, Color
X_OBJADDVERTEX 0.5,-0.5,0, 1,1, Color
X_OBJADDVERTEX 0.5,0.5,0, 1,0, Color

heres movement/rotation/scale code:

Code (glbasic) Select
FUNCTION EmitterSys_X_Trans3d: x,y,z , Scale , rx,ry,rz // x,y,z, Scale, Rx,Ry,Rz //move,scale,rotate an object
// This function Handles 3d inputs for,
// Move, Scale, Rotate for 3d objects.

X_SCALING Scale, Scale, Scale
IF rz<>0 THEN X_ROTATION rz,0,0,1
IF rx<>0 THEN X_ROTATION rx,1,0,0
IF ry<>0 THEN X_ROTATION ry,0,1,0

RETURN TRUE //pass completed, return=1 (BOOL=TRUE)

and heres the functions to properly rotate the particles to face the camera, or point a missle.

Code (glbasic) Select

@FUNCTION X_Vec2Rot: vX , vY , vZ
//Vector XYZ is the input, transforms to rotations, for use with X_Rotation .
//Object Face must be created towards +Z, so a camera IN +Z pointing to 0,0,0 sees the face.
//Returns rotations X and Y
// Billboarding:
//   Call these before X_ROTATION:
// DistanceX = CameraX - BillBoardX
// DistanceY = CameraY - BillBoardY
// DistanceZ = CameraZ - BillBoardZ
// X_Vector2Rot( DistanceX , DistanceX , DistanceZ )
// X_ROTATION AngleX2,1,0,0
// X_ROTATION AngleY2,0,1,0
// Missles Guidance:
//   This will use the vector Vector(dist per frame) of the missle to guide the rotations.
//   Just use the real 3d Vector:
// X_Vector2Rotation( VectorX , VectorX , VectorZ )
// X_ROTATION AngleX2,1,0,0
// X_ROTATION AngleY2,0,1,0
// AngleX2 AngleY2 are your global memories for the x_rotation

vX2 = X_Distance( 0.0 , vY , 0.0 , vX , vY , vZ )
AngleX = ATAN(-vX2 , -vY ) + 90.0
AngleY = ATAN( -vX , -vZ ) + 180.0


@FUNCTION X_Distance: x0,y0,z0, x1,y1,z1
//This function is used by FaceObject() Operations.
//It gives a distance between two points in 3d space.
//Vector 1 = x0,y0,z0
//Vector 2 = x1,y1,z1
// The return is the true distance between these 2 points. (Hypotenuese)

LOCAL x , y , z , xx , yy , zz
x  = x0 - x1; y  = y0 - y1; z  = z0 - z1;
xx = x*x; yy = y*y; zz = z*z;
RETURN SQR( xx + yy + zz )


goodluck, i have been banging my head for years on this.
Bing ChatGpt is pretty smart :O


Thanks for the tips :)

I did think about using a plane instead of x_sprite but wondered if there was a quicker way to keep x_sprite centred at x,y,z coords. I'll have a play and see what happens =D


Yay!! sorted out my particles using x_sprite and getting past the z-ordering issue  :good:

The z-ordering was a pain and wasn't making sense. What works for me is to draw all your 3D objects first. Then the last thing you draw is your particles. However, in order to get past the z-ordering issue I have to do a custom sort which is :

Code (glbasic) Select

// Particle[] is my array of type tParticle

SORTARRAY Particle[], ADDRESSOF(z_sort)

FOREACH blob in Particles[]
.... do your drawing of all particles - in my case X_SPRITE

Code (glbasic) Select

// tParticle is the type definition

FUNCTION z_sort:a AS tParticle, b AS tParticle
// CamX, Y, Z refers to the camera position
// Compare distance from camera particle to camera.
LOCAL temp1#, temp2#

temp1 = QSQR(((a.x - camX) * (a.x - camX)) + ((a.y - camY) * (a.y - camY)) + ((a.z - camZ) * (a.z - camZ)))
temp2 = QSQR(((b.x - camX) * (b.x - camX)) + ((b.y - camY) * (b.y - camY)) + ((b.z - camZ) * (b.z - camZ)))

IF temp1 > temp2 THEN RETURN -1
IF temp1 < temp2 THEN RETURN 1

Works spot on for me  :good:


nice work on the zorder function, PE's must use this in any case.

The problem im having with rendering is still visible due to opengl.
Maybe you know what i mean, when it looks like the particles run with a "choo choo train" visage as they move and die.
There is always one that overlaps all the other objects, no matter what, regardless of z order.
This is especially visible when firing hundreds of large overlapping particles moving on a path, that live and die in a second or two.
Maybe its just MY video cards?
Bing ChatGpt is pretty smart :O


I've noticed the outlines of particles when I use particles of vastly different sizes together. Luckily for what I need right now I'm OK with the above method as I only need a very basic particle system.

When my current game is finished though I *must* revisit this area as it's been driving me nuts and I *will* get it working properly  :P