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How do you make objects spin?

Started by Elite19 Nov 23, 2003 at 10:43 AM 4 replies 900+ views

Original Post

Nov 23, 2003 at 10:43 AM

Hi, I have made a simple model viewer with c# and mdx and I would like a button that makes whatever object is being displayed spin. Here is what I tried but it didn''t work //Globals static int iTime = Environment.TickCount % 1000; static float fAngle = iTime * (2.0f * (float)Math.PI) / 1000.0f; static Matrix ident = Matrix.Identity; static Matrix spin = Matrix.RotationY( fAngle ); Matrix crnt = ident; //Main loop static void Main() { using (WinForm frm = new WinForm()) { if (!frm.InitializeGraphics()) // Initialize Direct3D { MessageBox.Show("Could not initialize Direct3D. This tutorial will exit."); return; } frm.Show(); // While the form is still valid, render and process messages while(frm.Created) { frm.Render(); Application.DoEvents(); } } } The Render() meathod has a call to SetupMatrices() just after beginscene() //Setup matrices private void SetupMatrices() { device.Transform.World = crnt; device.Transform.View = Matrix.LookAtLH( new Vector3( 0.0f, 3.0f,-5.0f ), new Vector3( 0.0f, 0.0f, 0.0f ), new Vector3( 0.0f, 1.0f, 0.0f ) ); device.Transform.Projection = Matrix.PerspectiveFovLH( (float)Math.PI / 4, 1.0f, 1.0f, 100.0f ); } and finally the buttons event private void button1_Click(object sender, System.EventArgs e) { curnt = spin; } it compiles but the button does nothing. Any ideas? Thanks for this, it is greatly appreciated

Nik02

Nov 23, 2003 at 11:31 AM

curnt = spin;

Typo?

It's a good idea to keep strict declarations on, so that the compiler would warn you on writing to non-declared variables, such as this.

-Nik

[edited by - Nik02 on November 23, 2003 12:31:47 PM]

Elite19

Nov 23, 2003 at 7:17 PM

??
Yeah, that was just a typo here but its not in my code and it still doesn''t work.

Nik02

Nov 24, 2003 at 6:20 AM

I believe that
"static float fAngle = iTime * (2.0f * (float)Math.PI) / 1000.0f;"
results in 0 everytime, because it is initialized in the beginning of the program.

Move it to the click handler, as well as the part where you construct the rotation matrix.

EDIT:
In fact you should move all the time-related code to the click handler, instead of the app initialization. Remember that expressions are evaluated when, and only when, they are called.

EDIT2:
Here's some sample code on how i would tackle this problem.
Note that this is not the definite solution, but it'll make the geometry spin until you click the button again


//globals

bool bSpin = false;
int iTime = 0;

static void Main() 
{
using (WinForm frm = new WinForm())
{
if (!frm.InitializeGraphics()) // Initialize Direct3D

{
MessageBox.Show("Could not initialize Direct3D. This tutorial will exit.");
return;
}
frm.Show();

while(frm.Created)
{
frm.Render();
Application.DoEvents();
}
}
}

private void SetupMatrices()
{
if (bSpin) //if button has been clicked to indicate the desire to spin the geometry...

{
iTime = Environment.TickCount % 1000; //...update the time...

}

//...and make a rotation of that time unconditionally.

float fAngle = iTime * (2.0f * (float)Math.PI) / 1000.0f;
device.Transform.World = Matrix.RotationY( fAngle );

//then proceed as normal.

device.Transform.View = Matrix.LookAtLH( new Vector3( 0.0f, 3.0f,-5.0f ), new Vector3( 0.0f, 0.0f, 0.0f ), new Vector3( 0.0f, 1.0f, 0.0f ) );

device.Transform.Projection = Matrix.PerspectiveFovLH( (float)Math.PI / 4, 1.0f, 1.0f, 100.0f );
}

private void button1_Click(object sender, System.EventArgs e)
{
//crnt = spin;

bSpin != bSpin; //switch the spinning flag when button clicked


}

[edited by - Nik02 on November 24, 2003 7:38:42 AM]

ms291052

Nov 24, 2003 at 6:33 AM

You may want fAngle to be gloabal so just declare it globally (non-static, of course) and then modify it first thing in SetupMatrices. That way, like Nik02 said, it will be updated every frame instead of staying at zero.

Elite19

Nov 24, 2003 at 7:19 PM

Cool, Thanks Nik!!!

Works nicely
Now I think I''m getting the hang of this,
Thanks again

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