Create a two-dimensional polygon in XNA

Question

I have some kind of problem. I am new to XNA and want to draw a polygon shape that looks something like this (after all, I want this point to be random):

So, I read several articles, and this is what I ended up with:

private VertexPositionColor[] vertices; public TextureClass() { setupVertices(); } public override void Render(SpriteBatch spriteBatch) { Texture2D texture = createTexture(spriteBatch); spriteBatch.Draw(texture, new Rectangle((int)vertices[0].Position.X, (int)vertices[0].Position.Y, 30, 30), Color.Brown); } private Texture2D createTexture(SpriteBatch spriteBatch) { Texture2D texture = new Texture2D(spriteBatch.GraphicsDevice, 1, 1, false, SurfaceFormat.Color); texture.SetData<Color>(new Color[] { Color.Brown }); return texture; } 

When I call Render , it starts to draw some squares, as if they were in a loop. I just guess that I'm doing everything wrong. I would love it if someone pointed me in the right direction. Just create a polygon and draw it. It was that simple ...

Answer 1

This is what I have now.

The class that generates BasicEffect with some desired parameters.

 public class StandardBasicEffect : BasicEffect { public StandardBasicEffect(GraphicsDevice graphicsDevice) : base(graphicsDevice) { this.VertexColorEnabled = true; this.Projection = Matrix.CreateOrthographicOffCenter( 0, graphicsDevice.Viewport.Width, graphicsDevice.Viewport.Height, 0, 0, 1); } public StandardBasicEffect(BasicEffect effect) : base(effect) { } public BasicEffect Clone() { return new StandardBasicEffect(this); } } 

Here is my PolygonShape class

 /// <summary> /// A Polygon object that you will be able to draw. /// Animations are being implemented as we speak. /// </summary> /// <param name="graphicsDevice">The graphicsdevice from a Game object</param> /// <param name="vertices">The vertices in a clockwise order</param> public PolygonShape(GraphicsDevice graphicsDevice, VertexPositionColor[] vertices) { this.graphicsDevice = graphicsDevice; this.vertices = vertices; this.triangulated = false; triangulatedVertices = new VertexPositionColor[vertices.Length * 3]; indexes = new int[vertices.Length]; } /// <summary> /// Triangulate the set of VertexPositionColors so it will be drawn correcrly /// </summary> /// <returns>The triangulated vertices array</returns>} public VertexPositionColor[] Triangulate() { calculateCenterPoint();{ setupIndexes(); for (int i = 0; i < indexes.Length; i++) { setupDrawableTriangle(indexes[i]); } triangulated = true; return triangulatedVertices; } /// <summary> /// Calculate the center point needed for triangulation. /// The polygon will be irregular, so this isn't the actual center of the polygon /// but it will do for now, as we only need an extra point to make the triangles with</summary> private void calculateCenterPoint() { float xCount = 0, yCount = 0; foreach (VertexPositionColor vertice in vertices) { xCount += vertice.Position.X; yCount += vertice.Position.Y; } centerPoint = new Vector3(xCount / vertices.Length, yCount / vertices.Length, 0); } private void setupIndexes() { for (int i = 1; i < triangulatedVertices.Length; i = i + 3) { indexes[i / 3] = i - 1; } } private void setupDrawableTriangle(int index) { triangulatedVertices[index] = vertices[index / 3]; //No DividedByZeroException?... if (index / 3 != vertices.Length - 1) triangulatedVertices[index + 1] = vertices[(index / 3) + 1]; else triangulatedVertices[index + 1] = vertices[0]; triangulatedVertices[index + 2].Position = centerPoint; } /// <summary> /// Draw the polygon. If you haven't called Triangulate yet, I wil do it for you. /// </summary> /// <param name="effect">The BasicEffect needed for drawing</param> public void Draw(BasicEffect effect) { try { if (!triangulated) Triangulate(); draw(effect); } catch (Exception exception) { throw exception; } } private void draw(BasicEffect effect) { effect.CurrentTechnique.Passes[0].Apply(); graphicsDevice.DrawUserPrimitives<VertexPositionColor>( PrimitiveType.TriangleList, triangulatedVertices, 0, vertices.Length); } 

Sorry, this seems like a lot. Now for my next quest. Animation of my polygon.

Hope this helped other people with the same problem.

Answer 2

this code is useful for drawing 2D lines, some calculations can be done in the initialization call, but I prefer this example to keep everything together.

  public void DrawLine(VertexPositionColor[] Vertices) { Game.GraphicsDevice.DepthStencilState = DepthStencilState.Default; Vector2 center; center.X = Game.GraphicsDevice.Viewport.Width * 0.5f; center.Y = Game.GraphicsDevice.Viewport.Height * 0.5f; Matrix View = Matrix.CreateLookAt( new Vector3( center, 0 ), new Vector3( center, 1 ), new Vector3( 0, -1, 0 ) ); Matrix Projection = Matrix.CreateOrthographic( center.X * 2, center.Y * 2, -0.5f, 1 ); Effect EffectLines = Game.Content.Load<Effect>( "lines" ); EffectLines.CurrentTechnique = EffectLines.Techniques["Lines"]; EffectLines.Parameters["xViewProjection"].SetValue( View * Projection ); EffectLines.Parameters["xWorld"].SetValue( Matrix.Identity ); foreach ( EffectPass pass in EffectLines.CurrentTechnique.Passes ) { pass.Apply( ); Game.GraphicsDevice.DrawUserPrimitives<VertexPositionColor> ( PrimitiveType.LineList, Vertices, 0, Vertices.Length/2 ); } } 

LINES.FX

 uniform float4x4 xWorld; uniform float4x4 xViewProjection; void VS_Basico(in float4 inPos : POSITION, in float4 inColor: COLOR0, out float4 outPos: POSITION, out float4 outColor:COLOR0 ) { float4 tmp = mul (inPos, xWorld); outPos = mul (tmp, xViewProjection); outColor = inColor; } float4 PS_Basico(in float4 inColor:COLOR) :COLOR { return inColor; } technique Lines { pass Pass0 { VertexShader = compile vs_2_0 VS_Basico(); PixelShader = compile ps_2_0 PS_Basico(); FILLMODE = SOLID; CULLMODE = NONE; } } 

Answer 3

In the past, I worked with XNA in physical modeling, where I had to draw bounding fields using GraphicsDevice.DrawIndexedPrimitives (for more convenient examples, you should use Google or MSDN).

Below is the code I used in my project to draw 3D geometry.

 /// <summary> /// Draw the primitive. /// </summary> /// <param name="world">World Matrix</param> /// <param name="view">View Matrix</param> /// <param name="projection">Projection Matrix</param> /// <param name="color">Color of the primitive</param> public void Draw(Matrix world, Matrix view, Matrix projection, Color color) { _mGraphicsDevice.VertexDeclaration = _mVertexDeclaration; _mGraphicsDevice.Vertices[0].SetSource(_mVertexBuffer, 0, VertexPositionNormal.SizeInBytes); _mGraphicsDevice.Indices = _mIndexBuffer; _mBasicEffect.DiffuseColor = color.ToVector3(); _mBasicEffect.World = _mTransform * world; _mBasicEffect.View = view; _mBasicEffect.Projection = projection; int primitiveCount = _mIndex.Count / 3; _mBasicEffect.Begin(); foreach (EffectPass pass in _mBasicEffect.CurrentTechnique.Passes) { pass.Begin(); _mGraphicsDevice.DrawIndexedPrimitives(PrimitiveType.TriangleList, 0, 0, _mVertex.Count, 0, primitiveCount); pass.End(); } _mBasicEffect.End(); } 

This function is a member of a geometry object (class) and is called from a method of the Draw(GameTime) class of the Game