Simple Polygon in Box2d

[blandonfrank]

Adam,

Even though the polygons are been generated...their vertices are not drawn correctly.

I'm thinking it has to do with this:

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1. @Override
2.         protected void drawVertices(GL10 pGL, Camera pCamera)
3.         {
4.                 pGL.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, mVertices.length / 3);
5.         }

Parsed in 0.031 seconds, using GeSHi 1.0.8.4

[Radzell]

Is there anyway you can make pass vector2 arrays?

[blandonfrank]

Well, I think it's possible to do it. But, then you'll have to add the Vector2 class to the engine as it's not there.

[Radzell]

Mayby you can use a PointF and then find a way to turn a PointF to Vector2

[blandonfrank]

Possibly. But, why do you want to use Vector2?

[Radzell]

because create from polygon when make a b2body use vector2 so you could pass the some vertice to both and it would give you a exact same shape in the physics and andengine world.

[Nicolas Gramlich]

Hi guys,

I currently only see the need for such an untextured "Polygon"-class. "Unfortunately" quite a couple of thing need to know the width and height of such a shape which isn't trivial anymore for Polygons. In most of the cases it will be so much simpler to achieve a complex looking polygon, by using a textured sprite.

Best Regards,
Nicolas

[Mimminito]

Yes I know what you mean Nicolas, I was doing this for two reasons:
1. My own personal knowledge and gain. So I could edit AndEngine and have something workable at the end.
2. Personal preference. Its nice to be able to do something without textures for once. Then creating the textures when its finalised is an easy option.

[ichi]

Anyone who has made a newer version of this? I can draw polygons using this but I don't understand the positioning. I've looked a bit at "Line.java" for reference and it seems that the draw positions (polygonvertexbuffer values for each vertex) are wrong.

I'm trying to fix this myself but I'm getting nowhere atm, does anyone have an already fixed updated version of this Polygon?

Edit: Sorry, think I was wrong. I think the previous examples on how to define the vertices in this post was wrong but I'm gonna try some more to see if I'm right.

Ya, this is just wrong:

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1. #
2. float[] vertices = {
3.  180f, -180f, 0.0f,
4.  180f, 180f, 0.0f,
5. -180f, -180f, 0.0f,};

Parsed in 0.030 seconds, using GeSHi 1.0.8.4

This is proper I think, makes the same "result" as above:

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1. #
2. float[] vertices = {
3.  180f, -180f,
4.  0.0f, 180f,
5.  180f, 0.0f};

Parsed in 0.034 seconds, using GeSHi 1.0.8.4

[chozabu]

Ichi - The column of 0.0f is because opengl is 3d - it is the z Co-ord.

The code from a page or two ago did not seem to compile with the latest andengine from git, so here it is with my (tiny) updates

Nice one for writing this Mimminito!

the test poly blandonfrank provided displays fine, once I have my level data loading correctly I'll see if I can add texturing support

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1. package org.anddev.andengine.entity.primitive;
2.  
3. import javax.microedition.khronos.opengles.GL10;
4. import javax.microedition.khronos.opengles.GL11;
5.  
6. import org.anddev.andengine.engine.camera.Camera;
7. import org.anddev.andengine.entity.shape.GLShape;
8. import org.anddev.andengine.entity.shape.IShape;
9. import org.anddev.andengine.opengl.buffer.BufferObjectManager;
10. import org.anddev.andengine.opengl.util.GLHelper;
11. import org.anddev.andengine.opengl.vertex.PolygonVertexBuffer;
12. import org.anddev.andengine.opengl.vertex.VertexBuffer;
13.  
14. public class Polygon extends GLShape
15. {
16.        
17.         // ===========================================================
18.         // Fields
19.         // ===========================================================
20.        
21.         private float[] mVertices;
22.        
23.         private final PolygonVertexBuffer mPolygonVertexBuffer;
24.        
25.         // ===========================================================
26.         // Constructors
27.         // ===========================================================
28.  
29.         public Polygon(float pX, float pY, float[] pVertices)
30.         {
31.                 this(pX, pY, pVertices, new PolygonVertexBuffer(pVertices.length, GL11.GL_STATIC_DRAW));
32.         }
33.        
34.         public Polygon(float pX, float pY, float[] pVertices, final PolygonVertexBuffer pPolygonVertexBuffer)
35.         {
36.                 super(pX, pY);
37.                
38.                 this.mVertices = pVertices;
39.                
40.                 this.mPolygonVertexBuffer = pPolygonVertexBuffer;
41.                 BufferObjectManager.getActiveInstance().loadBufferObject(this.mPolygonVertexBuffer);
42.                 this.updateVertexBuffer();
43.         }
44.        
45.         // ===========================================================
46.         // Getter & Setter
47.         // ===========================================================
48.        
49.         // ===========================================================
50.         // Methods for/from SuperClass/Interfaces
51.         // ===========================================================
52.        
53.         @Override
54.         protected void onInitDraw(GL10 pGL)
55.         {
56.                 super.onInitDraw(pGL);
57.                 GLHelper.disableTextures(pGL);
58.                 GLHelper.disableTexCoordArray(pGL);            
59.         }
60.        
61.         @Override
62.         protected VertexBuffer getVertexBuffer()
63.         {
64.                 return this.mPolygonVertexBuffer;
65.         }
66.  
67.         @Override
68.         protected void onUpdateVertexBuffer()
69.         {
70.                 this.mPolygonVertexBuffer.update(mVertices);
71.         }
72.  
73.         @Override
74.         protected void drawVertices(GL10 pGL, Camera pCamera)
75.         {
76.                 pGL.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, mVertices.length / 3);
77.         }
78.  
79.         @Override
80.         protected boolean isCulled(Camera pCamera)
81.         {
82.                 // TODO Auto-generated method stub
83.                 return false;
84.         }
85.  
86.         @Override
87.         public boolean collidesWith(IShape pOtherShape)
88.         {
89.                 // TODO Auto-generated method stub
90.                 return false;
91.         }
92.  
93.         @Override
94.         public float getBaseHeight()
95.         {
96.                 // TODO Auto-generated method stub
97.                 return 0;
98.         }
99.  
100.         @Override
101.         public float getBaseWidth()
102.         {
103.                 // TODO Auto-generated method stub
104.                 return 0;
105.         }
106.  
107.         @Override
108.         public float getHeight()
109.         {
110.                 // TODO Auto-generated method stub
111.                 return 0;
112.         }
113.  
114.         @Override
115.         public float[] getSceneCenterCoordinates()
116.         {
117.                 // TODO Auto-generated method stub
118.                 return null;
119.         }
120.  
121.         @Override
122.         public float getWidth()
123.         {
124.                 // TODO Auto-generated method stub
125.                 return 0;
126.         }
127.  
128.         @Override
129.         @Deprecated
130.         public boolean contains(float pX, float pY)
131.         {
132.                 return false;
133.         }
134.  
135.         @Override
136.         @Deprecated
137.         public float[] convertLocalToSceneCoordinates(float pX, float pY)
138.         {
139.                 return null;
140.         }
141.  
142.         @Override
143.         @Deprecated
144.         public float[] convertSceneToLocalCoordinates(float pX, float pY)
145.         {
146.                 return null;
147.         }
148.  
149. }
150.  
151.  

Parsed in 0.047 seconds, using GeSHi 1.0.8.4

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Using java Syntax Highlighting

1. package org.anddev.andengine.opengl.vertex;
2.  
3. //import java.nio.FloatBuffer;
4.  
5. import org.anddev.andengine.opengl.util.FastFloatBuffer;
6.  
7. public class PolygonVertexBuffer extends VertexBuffer
8. {
9.  
10.         final static int BYTES_PER_FLOAT = Float.SIZE/8;
11.         public PolygonVertexBuffer(int pVerticesCount, int pDrawType)
12.         {
13.                 super(2 * pVerticesCount * BYTES_PER_FLOAT, pDrawType);
14.         }
15.        
16.         public void update(float[] pVertices)
17.         {
18.                 final FastFloatBuffer buffer = this.getFloatBuffer();
19.                 buffer.position(0);
20.                
21.                 buffer.put(pVertices);
22.                
23.                 buffer.position(0);
24.                
25.                 //super.update();
26.         }
27. }
28.  
29.  

Parsed in 0.037 seconds, using GeSHi 1.0.8.4