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Recursive calls with pass-by-reference indexers!


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#1 MatsK   Members   -  Reputation: 263

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Posted 06 March 2012 - 04:12 AM

I'm trying to render a skeleton to the screen, and making it render properly requires me to use recursion and pass by reference. But I can't do that, because I get the error A property or indexer may not be passed as an out or ref parameter.
Here's what I'm trying to do:

public static void DrawBonesSkeleton(ref Bone Bne)
		{
			Gl.glPointSize(5.0f);
			Gl.glTranslatef(Bne.GlobalTranslation.X, Bne.GlobalTranslation.Y, Bne.GlobalTranslation.Z);
			float[] RotationMatrix = FindQuaternionMatrix(Bne.GlobalRotation);
			Gl.glMultMatrixf(RotationMatrix);
			if (Bne.BoneName == "ROOT")
				Gl.glColor3f(1.0f, 0.0f, 0.0f);
			else if (Bne.BoneName == "HEAD")
				Gl.glColor3f(1.0f, 1.0f, 0.0f);
			else
				Gl.glColor3f(0.0f, 1.0f, 0.0f);
			Gl.glBegin(Gl.GL_POINTS); Gl.glVertex3f(0, 0, 0); Gl.glEnd();
			if (Bne.Children.Count == 1)
				DrawBonesSkeleton(ref Bne.Children[0]);
			else if (Bne.Children.Count > 1)
			{
				for (int i = 0; i < Bne.Children.Count; i++)
					DrawBonesSkeleton(ref Bne.Children[i]);
			}
		}

The original code is:

void DrawBonesSkeleton(Bone_t& Bone)
341 {
342	 glPointSize(5.0);
343	 glTranslatef(Bone.Translation.x, Bone.Translation.y, Bone.Translation.z);
344	 float RotationMatrix[16];
345	 FindQuaternionMatrix(RotationMatrix, &Bone.Rotation);
346	 glMultMatrixf(RotationMatrix);
347
348	 if(!strcmp(Bone.Name, "ROOT"))
349		 glColor3f(1.0, 0.0, 0.0);
350	 else if(!strcmp(Bone.Name, "HEAD"))
351		 glColor3f(1.0, 1.0, 0.0);
352	 else
353		 glColor3f(0.0, 1.0, 0.0);
354	 glBegin(GL_POINTS); glVertex3f(0, 0, 0); glEnd();
355
356	 if(Bone.ChildrenCount == 1){
357		 DrawBonesSkeleton(*Bone.Children[0]);
358	 }else if(Bone.ChildrenCount > 1){
359		 for(unsigned i=0; i<Bone.ChildrenCount; i++){
360			 glPushMatrix();
361			 DrawBonesSkeleton(*Bone.Children[i]);
362			 glPopMatrix();
363		 }
364	 }
365 }

Please keep in mind that I'm trying to do this *without* pointers. Pointers are my last resort. Is there any way to get around this problem, or am I stuck with having to use pointers?

Note: I already tried looping through the bones using foreach, but it results in the skeleton being rendered incorrectly.

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#2 MatsK   Members   -  Reputation: 263

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Posted 06 March 2012 - 11:18 PM

I figured out how to do this. Turns out you cannot pass elements of List<> by reference, but you *can* pass elements of a normal array by reference!

#3 Washu   Senior Moderators   -  Reputation: 5447

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Posted 06 March 2012 - 11:34 PM

If you have a List<> of structures then the structures are pass-by-value. Since operator[] is actually a method call into List<> this ends up returning an unnamed temporary value that is a copy of the structure contained in the list (not the structure in the list). You cannot take a reference to an unnamed temporary.

In time the project grows, the ignorance of its devs it shows, with many a convoluted function, it plunges into deep compunction, the price of failure is high, Washu's mirth is nigh.
ScapeCode - Blog | SlimDX


#4 Nitage   Members   -  Reputation: 810

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Posted 07 March 2012 - 04:43 PM

You don't need to use the ref keyword at all, seeing as you're not assigning to the bne parameter.

Also, keep in mind that in C# parameters of a class type are automatically passed by reference and using the ref keyword creates a reference to a reference.

#5 MatsK   Members   -  Reputation: 263

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Posted 08 March 2012 - 05:11 AM

I do need to use ref, the skeleton isn't drawn correctly otherwise. I don't fully understand the skeleton format though, both the skeleton and mesh format is proprietary and AAA (used by The Sims and TSO). I think it might have something to do with the fact that the bones' rotation is normalized (a normalized quaternion, referred to as a 'vertor').

#6 Telastyn   Crossbones+   -  Reputation: 3730

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Posted 08 March 2012 - 12:28 PM

I do need to use ref, the skeleton isn't drawn correctly otherwise.


Then there's an error elsewhere in your code.

#7 MatsK   Members   -  Reputation: 263

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Posted 10 March 2012 - 04:17 AM

Ok?

using System;
using System.Collections.Generic;
using System.Text;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Runtime.InteropServices;
using SFML;
using SFML.Graphics;
using SFML.Window;
using Tao.Glfw;
using Tao.OpenGl;
namespace SFML_test
{
    class Program
    {
	    private static Character[] m_Characters;
	    private static float m_Zoom = -20.0f;
	    private static int[] m_VertexBuffer = new int[1];
	    private static int[] m_TextureBuffer = new int[1];
	    private static int[] m_IndexBuffer = new int[1];
	    private static float m_TimeDelta = 0.0f;
	    static void Main(string[] args)
	    {
		    // Create main window
		    RenderWindow App = new RenderWindow(new VideoMode(800, 600), "Project Dollhouse SFML.Net Test");
		    App.PreserveOpenGLStates(true);
		    App.Resized += new EventHandler<SizeEventArgs>(App_Resized);
		    App.KeyPressed += new EventHandler<KeyEventArgs>(App_KeyPressed);
		    m_Characters = new Character[1];
		   
		    Character Char = new Character();
		    Char.Translation = new Vector3(0.0f, -1.5f, 0.0f);
		    Char.Rotation = new Quaternion(0.0f, 0.0f, 0.0f, 0.0f);
		    Char.BodyMesh = new Mesh("data\\pelvis-body.mesh", true);
		    Char.BodyTexture = new SFML.Graphics.Image("data\\body.jpg");
		    Char.Skel = new Skeleton("data\\adult.skel");
		    Char.Skel.AssignChildren(ref Char.Skel);
		    Char.CurrentAnimation = new Anim("data\\a2a-dancee-loop-whip.anim");
		    m_Characters[0] = Char;
		    /*=========================================================================================*/
		    /* Requirement: Being able to load compressed BMPs.
			 * ========================================================================================*/
		    System.Drawing.Image Img = System.Drawing.Image.FromFile("data\\person_select_background.bmp");
		    MemoryStream ImgStream = new MemoryStream();
		    Img.Save(ImgStream, ImageFormat.Jpeg);
		    // Create a sprite for the background
		    SFML.Graphics.Image BackgroundImage = new SFML.Graphics.Image(ImgStream);
		    Sprite Background = new Sprite(BackgroundImage);
		    /*==========================================================================================*/
		    /* Requirement: Being able to seamlessly combine OpenGL and SFML-calls
			 * =========================================================================================*/
		    Gl.glShadeModel(Gl.GL_SMOOTH);
		 Gl.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
		 Gl.glClearDepth(1.0f);
		 Gl.glEnable(Gl.GL_DEPTH_TEST);
		 Gl.glEnable(Gl.GL_CULL_FACE);
		 Gl.glEnable(Gl.GL_RESCALE_NORMAL);
		 Gl.glDisable(Gl.GL_BLEND);
		 Gl.glDepthFunc(Gl.GL_LEQUAL);
		 Gl.glHint(Gl.GL_PERSPECTIVE_CORRECTION_HINT, Gl.GL_NICEST);
		    Gl.glViewport(0, 0, 800, 600);
		    // Setup a perspective projection
		    Gl.glMatrixMode(Gl.GL_PROJECTION);
		    Gl.glLoadIdentity();
		    Glu.gluPerspective(45.0F, (float)800 / 600, 0.1F, 100.0F);
		    Gl.glMatrixMode(Gl.GL_MODELVIEW);
		    Gl.glLoadIdentity();
		    while (App.IsOpened())
		    {
			    // Set the active window before using OpenGL commands
			    // It's useless here because the active window is always the same,
			    // but don't forget it if you use multiple windows
			    App.SetActive();
			    // Process events
			    App.DispatchEvents();
			    // Clear the window
			    App.Clear();
			    //Clear the screen and the depth buffer
			    Gl.glClear(Gl.GL_COLOR_BUFFER_BIT | Gl.GL_DEPTH_BUFFER_BIT);
			    // Draw background
			    App.Draw(Background);
			    m_TimeDelta = App.GetFrameTime();
			    foreach (Character Sim in m_Characters)
			    {
				    Gl.glLoadIdentity();
				    Gl.glTranslatef(Sim.Translation.X, Sim.Translation.Y, m_Zoom + Sim.Translation.Z);
				    Gl.glRotatef(Sim.Rotation.X, 1.0f, 0.0f, 0.0f);
				    Gl.glRotatef(Sim.Rotation.Y, 0.0f, 1.0f, 0.0f);
				    Gl.glRotatef(Sim.Rotation.Z, 0.0f, 0.0f, 1.0f);
				    Gl.glPolygonMode(Gl.GL_FRONT_AND_BACK, Gl.GL_FILL);
				    Gl.glColor3f(1.0f, 1.0f, 1.0f);
				    DrawMeshes(Sim);
				    Gl.glClear(Gl.GL_DEPTH_BUFFER_BIT);
				    DrawSkeleton(Sim.Skel);
			    }
			    App.Display();
		    }
	    }
	    private static void App_KeyPressed(object sender, KeyEventArgs e)
	    {
		    if (e.Code == KeyCode.N)
		    {
			    m_Characters[0].AdvanceFrame(m_TimeDelta);
		    }
	    }
	    private static void App_Resized(object sender, SizeEventArgs e)
	    {
		    if (e.Height == 0)
			    e.Height++;
		    Gl.glShadeModel(Gl.GL_SMOOTH);
		    Gl.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
		    Gl.glClearDepth(1.0f);
		    Gl.glEnable(Gl.GL_DEPTH_TEST);
		    Gl.glEnable(Gl.GL_CULL_FACE);
		    Gl.glEnable(Gl.GL_RESCALE_NORMAL);
		    Gl.glDisable(Gl.GL_BLEND);
		    Gl.glDepthFunc(Gl.GL_LEQUAL);
		    Gl.glHint(Gl.GL_PERSPECTIVE_CORRECTION_HINT, Gl.GL_NICEST);
		    Gl.glViewport(0, 0, 800, 600);
		    // Setup a perspective projection
		    Gl.glMatrixMode(Gl.GL_PROJECTION);
		    Gl.glLoadIdentity();
		    Glu.gluPerspective(45.0F, (float)800 / (float)600, 0.1F, 100.0F);
		    Gl.glMatrixMode(Gl.GL_MODELVIEW);
		    Gl.glLoadIdentity();
	    }
	    private static void DrawMeshes(Character Sim)
	    {
		    Gl.glPointSize(2.0f);
		    Gl.glColor3f(1.0f, 1.0f, 1.0f);
		    Gl.glPushMatrix();
		    Gl.glLoadIdentity();
		    Sim.BodyMesh.TransformVertices2(ref Sim.Skel.Bones[0]);
		    Gl.glPopMatrix();
		    Sim.BodyMesh.BlendVertices2();
		    Gl.glEnable(Gl.GL_TEXTURE_2D);
		    Gl.glEnableClientState(Gl.GL_VERTEX_ARRAY);
		    Gl.glEnableClientState(Gl.GL_TEXTURE_COORD_ARRAY);
		    Sim.BodyTexture.Bind();
		    unsafe
		    {
			    fixed (Vector3* Ptr = &Sim.BodyMesh.TransformedVertices[0])
				    Gl.glVertexPointer(3, Gl.GL_FLOAT, (int)Marshal.SizeOf(typeof(Vector3)), (IntPtr)Ptr);
			    fixed (Vector2* Ptr = &Sim.BodyMesh.TransformedTexVertices[0])
				    Gl.glTexCoordPointer(2, Gl.GL_FLOAT, Marshal.SizeOf(typeof(Vector2)), (IntPtr)Ptr);
			    Gl.glDrawElements(Gl.GL_TRIANGLES, Sim.BodyMesh.FaceCount * 3, Gl.GL_UNSIGNED_INT,
				    Sim.BodyMesh.FaceIndexes);
		    }
		    Gl.glDisableClientState(Gl.GL_VERTEX_ARRAY);
		    Gl.glDisableClientState(Gl.GL_TEXTURE_COORD_ARRAY);
		    Gl.glDisable(Gl.GL_TEXTURE_2D);
	    }
	    private static void DrawSkeleton(Skeleton Skel)
	    {
		    Gl.glPushMatrix();
		    DrawBonesSkeleton(ref Skel.Bones[0]);
		    Gl.glPopMatrix();
	    }
	    private static void DrawBonesSkeleton(ref Bone Bne)
	    {
		    Gl.glPointSize(5.0f);
		    Gl.glTranslatef(Bne.GlobalTranslation.X, Bne.GlobalTranslation.Y, Bne.GlobalTranslation.Z);
		    float[] RotationMatrix = FindQuaternionMatrix(Bne.GlobalRotation);
		    Gl.glMultMatrixf(RotationMatrix);
		    if (Bne.BoneName == "ROOT")
			    Gl.glColor3f(1.0f, 0.0f, 0.0f);
		    else if (Bne.BoneName == "HEAD")
			    Gl.glColor3f(1.0f, 1.0f, 0.0f);
		    else
			    Gl.glColor3f(0.0f, 1.0f, 0.0f);
		    Gl.glBegin(Gl.GL_POINTS); Gl.glVertex3f(0, 0, 0); Gl.glEnd();
		    if (Bne.NumChildren == 1)
			    DrawBonesSkeleton(ref Bne.Children[0]);
		    else if (Bne.NumChildren > 1)
		    {
			    for (int i = 0; i < Bne.NumChildren; i++)
			    {
				    Gl.glPushMatrix();
				    DrawBonesSkeleton(ref Bne.Children[i]);
				    Gl.glPopMatrix();
			    }
		    }
	    }
	    private static float[] FindQuaternionMatrix(Quaternion Rotation)
	    {
		    float[] Matrix = new float[16];
		    float X2 = Rotation.X * Rotation.X;
		    float Y2 = Rotation.Y * Rotation.Y;
		    float Z2 = Rotation.Z * Rotation.Z;
		    float XY = Rotation.X * Rotation.Y;
		    float XZ = Rotation.X * Rotation.Z;
		    float YZ = Rotation.Y * Rotation.Z;
		    float WX = Rotation.W * Rotation.X;
		    float WY = Rotation.W * Rotation.Y;
		    float WZ = Rotation.W * Rotation.Z;
		    Matrix[0] = 1.0f - 2.0f * (Y2 + Z2);
		    Matrix[1] = 2.0f * (XY - WZ);
		    Matrix[2] = 2.0f * (XZ + WY);
		    Matrix[3] = 0.0f;
		    Matrix[4] = 2.0f * (XY + WZ);
		    Matrix[5] = 1.0f - 2.0f * (X2 + Z2);
		    Matrix[6] = 2.0f * (YZ - WX);
		    Matrix[7] = 0.0f;
		    Matrix[8] = 2.0f * (XZ - WY);
		    Matrix[9] = 2.0f * (YZ + WX);
		    Matrix[10] = 1.0f - 2.0f * (X2 + Y2);
		    Matrix[11] = 0.0f;
		    Matrix[12] = 0.0f;
		    Matrix[13] = 0.0f;
		    Matrix[14] = 0.0f;
		    Matrix[15] = 1.0f;
		    return Matrix;
	    }
    }
}





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