Java-Gaming.org Hi !
 Featured games (84) games approved by the League of Dukes Games in Showcase (569) Games in Android Showcase (154) games submitted by our members Games in WIP (618) games currently in development
 News: Read the Java Gaming Resources, or peek at the official Java tutorials
Pages: [1]
 ignore  |  Print
 Calculating rotated points of a rectangle  (Read 1688 times) 0 Members and 1 Guest are viewing this topic.
PRW56

Senior Newbie

 « Posted 2013-10-31 17:01:30 »

Hello, I am using vertex buffers to draw this at the moment, but for some reason after the program is launched, the thing that is being drawn appears in the top left corner (close to 0,0) when it is supposed to be at (100,100). The sprite is being rotated around a point Center (a Vector 2), and the Center is being set to (X + (width of sprite)/2) and (Y + (height of sprite/2)) every time the x or y of the sprite is being changed. When I made it so that the rotation (which up until this point had been set at 0) increased every frame, the sprite seemed to rotate around a point close to (0,0). Is there a way I am calculating the new position wrong? Ty for any help!

Position is a Vector 3 by the way and although a Z is in there I am only doing 2D things right now

here is code for calculating verticies:
 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31 `float x, y;         float cosRot = FMath.Cos(Rotation);         float sinRot = FMath.Sin(Rotation);                  // Point 1 - top left         x = Position.X - Center.X;         y = Position.Y - Center.Y;         vertices[0]=(float)(x*cosRot - y*sinRot);   // x0         vertices[1]=(float)(x*sinRot + y*cosRot);   // y0         vertices[2]=Position.Z;                  // z0                  // Point 2 - bottom left         x = Position.X - Center.X;         y = (Position.Y + height) - Center.Y;         vertices[3]=(float)(x*cosRot - y*sinRot);   // x1         vertices[4]=(float)(x*sinRot + y*cosRot);// y1         vertices[5]=Position.Z;                  // z1                  // Point 3 - top right         x = (Position.X + width) - Center.X;         y = Position.Y - Center.Y;         vertices[6]=(float)(x*cosRot - y*sinRot);   // x2         vertices[7]=(float)(x*sinRot + y*cosRot);      // y2         vertices[8]=Position.Z;                     // z2                  // Point 4 - bottom right         x = (Position.X + width) - Center.X;         y = (Position.Y + height) - Center.Y;         vertices[9]=(float)(x*cosRot - y*sinRot);   // x3         vertices[10]=(float)(x*sinRot + y*cosRot);// y3         vertices[11]=Position.Z;               // z3`
Rakiayn

Senior Newbie

 « Reply #1 - Posted 2013-10-31 19:58:44 »

you might want to check out this post
http://www.java-gaming.org/topics/rotation-matrix-example/30834/view.html
you can use the code in the second to last post by drzoidberg.
the rotation matrix is for 3d. but you can use it for 2d too.
RobinB

JGO Ninja

Medals: 44
Projects: 1
Exp: 3 years

Spacegame in progress

 « Reply #2 - Posted 2013-10-31 21:27:38 »

I made a function like this a while ago, maybe you could use it:

 1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19 `    public static Vector2f[] rotate(Vector4f src, float rotation){        Vector2f[] dst = new Vector2f[4];        float sin = FastMath.sinf(rotation);        float cos = FastMath.cosf(rotation);        float wsin = sin * (src.z / 2);        float wcos = cos * (src.z / 2);        float hsin = sin * (src.w / 2);        float hcos = cos * (src.w / 2);        //x' = x*cos(t) - y*sin(t)        //y' = x*sin(t) + y*cos(t)        dst[0] = new Vector2f(src.x + wcos - hsin, src.y + hcos + wsin);        dst[1] = new Vector2f(src.x - wcos - hsin, src.y + hcos - wsin);        dst[2] = new Vector2f(src.x + wcos + hsin, src.y - hcos + wsin);        dst[3] = new Vector2f(src.x - wcos + hsin, src.y - hcos - wsin);        return dst;    }`
Pages: [1]
 ignore  |  Print

You cannot reply to this message, because it is very, very old.

 Riven (23 views) 2015-04-16 10:48:47 Duke0200 (36 views) 2015-04-16 01:59:01 Fairy Tailz (27 views) 2015-04-14 20:13:12 Riven (29 views) 2015-04-12 21:36:37 bus hotdog (46 views) 2015-04-10 02:39:32 CopyableCougar4 (47 views) 2015-04-10 00:51:04 BurntPizza (48 views) 2015-04-06 22:06:58 ags1 (51 views) 2015-04-02 10:58:48 Riven (49 views) 2015-04-01 18:27:05 ags1 (66 views) 2015-03-31 10:55:12
 BurntPizza 24x theagentd 21x wessles 15x 65K 12x Rayvolution 12x kingroka123 11x alwex 10x KevinWorkman 9x kevglass 8x ra4king 8x phu004 8x Hanksha 7x SHC 7x Olo 7x Ecumene 7x chrislo27 7x
 How to: JGO Wikiby Mac702015-02-17 20:56:162D Dynamic Lighting2015-01-01 20:25:42How do I start Java Game Development?by gouessej2014-12-27 19:41:21Resources for WIP gamesby kpars2014-12-18 10:26:14Understanding relations between setOrigin, setScale and setPosition in libGdx2014-10-09 22:35:00Definite guide to supporting multiple device resolutions on Android (2014)2014-10-02 22:36:02List of Learning Resources2014-08-16 10:40:00List of Learning Resources2014-08-05 19:33:27
 java-gaming.org is not responsible for the content posted by its members, including references to external websites, and other references that may or may not have a relation with our primarily gaming and game production oriented community. inquiries and complaints can be sent via email to the info‑account of the company managing the website of java‑gaming.org