World position of vertex?

[DruggedBunnyParticipant]

How do I get hold of the world position of a mesh’s vertex? I’m trying to visualise a terrain’s vertices, and have got my mesh vertices easily enough, but it’s just the ‘raw’ mesh vertices rather than their current position in space…

See DrawVertices:

Monkey

[crayon-5cb9c3b4f41f3982901599 inline="true" ] #Import "<std>" #Import "<mojo3d>" Using std.. Using mojo.. Using mojo3d.. ' ---------------------------------------- ' Application name... ' ---------------------------------------- Global AppName:String = "My 3D Game" Class Model Extension Method DrawVertices:Void (canvas:Canvas, from_camera:Camera) For Local v:Vertex3f = Eachin Mesh.GetVertices () Local v2:Vec2f = from_camera.ProjectToViewport (v.position) canvas.DrawRect (v2.x, v2.y, 1, 1) Next End End Class Game Extends Window Const SHIFT_BOOST:Float = 5.0 Field camera_boost:Float = 1.0 ' Basic 3D scene requirements... Field scene:Scene Field camera:Camera Field light:Light ' Test cube... Field cube:Model Field cubemesh:Mesh Field cubematerial:Material Method New (title:String, width:Int, height:Int, flags:WindowFlags) Super.New (title, width, height, flags) scene = Scene.GetCurrent () ' Important! camera = New Camera ' Camera settings... camera.Near = 0.1 ' Camera position... camera.Move (0, 0, -2) camera.Rotate (0, 0, 0) light = New Light light.Move (-10, 10, -10) light.Rotate (0, 0, 0) cubemesh = Mesh.CreateBox (New Boxf (-0.5, -0.5, -0.5, 0.5, 0.5, 0.5)) ' 1 x 1 x 1 cubematerial = New PbrMaterial (Color.Aluminum) cube = New Model (cubemesh, cubematerial) cube.Rotate (0, 45, 0) End Method UpdateGame:Void () End Method OnRender (canvas:Canvas) Override ProcessInput () UpdateGame () cube.Rotate (0.0, 1.0, 0.0) ' Tell app to draw frame when ready... RequestRender () ' Render scene to canvas (passed to OnRender by mojo), from camera... scene.Render (canvas) cube.DrawVertices (canvas, camera) End Method ProcessInput:Void () If Keyboard.KeyHit (Key.Space) Then light.CastsShadow = Not light.CastsShadow If Keyboard.KeyDown (Key.LeftShift) camera_boost = SHIFT_BOOST Else camera_boost = 1.0 Endif If Keyboard.KeyHit (Key.Escape) Then App.Terminate () If Keyboard.KeyDown (Key.A) camera.Move (0.0, 0.0, 0.1 * camera_boost) Endif If Keyboard.KeyDown (Key.Z) camera.Move (0.0, 0.0, -0.1 * camera_boost) Endif If Keyboard.KeyDown (Key.Left) camera.Rotate (0.0, 1.0, 0.0) Endif If Keyboard.KeyDown (Key.Right) camera.Rotate (0.0, -1.0, 0.0) Endif If Keyboard.KeyDown (Key.Up) camera.Rotate (1.0, 0.0, 0.0, True) Endif If Keyboard.KeyDown (Key.Down) camera.Rotate (-1.0, 0.0, 0.0, true) Endif End End Function Main () ' Windowed mode... Local width:Int = 640 Local height:Int = 480 Local flags:WindowFlags = WindowFlags.Center ' Full-screen mode (comment out above)... ' Local width:Int = 1920 ' Local height:Int = 1080 ' Local flags:WindowFlags = WindowFlags.Fullscreen New AppInstance New Game (AppName, width, height, flags) App.Run () End

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[crayon-5cb9c3b4f41f3982901599 inline="true" ]   #Import "<std>" #Import "<mojo3d>"   Using std.. Using mojo.. Using mojo3d..   ' ---------------------------------------- ' Application name... ' ----------------------------------------   Global AppName:String = "My 3D Game"   Class Model Extension   Method DrawVertices:Void (canvas:Canvas, from_camera:Camera) For Local v:Vertex3f = Eachin Mesh.GetVertices () Local v2:Vec2f = from_camera.ProjectToViewport (v.position) canvas.DrawRect (v2.x, v2.y, 1, 1) Next End End   Class Game Extends Window Const SHIFT_BOOST:Float = 5.0 Field camera_boost:Float = 1.0 ' Basic 3D scene requirements... Field scene:Scene Field camera:Camera Field light:Light ' Test cube... Field cube:Model Field cubemesh:Mesh Field cubematerial:Material Method New (title:String, width:Int, height:Int, flags:WindowFlags) Super.New (title, width, height, flags) scene = Scene.GetCurrent () ' Important! camera = New Camera ' Camera settings... camera.Near = 0.1 ' Camera position... camera.Move (0, 0, -2) camera.Rotate (0, 0, 0) light = New Light light.Move (-10, 10, -10) light.Rotate (0, 0, 0) cubemesh = Mesh.CreateBox (New Boxf (-0.5, -0.5, -0.5, 0.5, 0.5, 0.5)) ' 1 x 1 x 1 cubematerial = New PbrMaterial (Color.Aluminum) cube = New Model (cubemesh, cubematerial) cube.Rotate (0, 45, 0) End Method UpdateGame:Void () End Method OnRender (canvas:Canvas) Override ProcessInput () UpdateGame () cube.Rotate (0.0, 1.0, 0.0) ' Tell app to draw frame when ready... RequestRender () ' Render scene to canvas (passed to OnRender by mojo), from camera... scene.Render (canvas)   cube.DrawVertices (canvas, camera)   End   Method ProcessInput:Void ()   If Keyboard.KeyHit (Key.Space) Then light.CastsShadow = Not light.CastsShadow   If Keyboard.KeyDown (Key.LeftShift) camera_boost = SHIFT_BOOST Else camera_boost = 1.0 Endif If Keyboard.KeyHit (Key.Escape) Then App.Terminate () If Keyboard.KeyDown (Key.A) camera.Move (0.0, 0.0, 0.1 * camera_boost) Endif If Keyboard.KeyDown (Key.Z) camera.Move (0.0, 0.0, -0.1 * camera_boost) Endif If Keyboard.KeyDown (Key.Left) camera.Rotate (0.0, 1.0, 0.0) Endif If Keyboard.KeyDown (Key.Right) camera.Rotate (0.0, -1.0, 0.0) Endif If Keyboard.KeyDown (Key.Up) camera.Rotate (1.0, 0.0, 0.0, True) Endif If Keyboard.KeyDown (Key.Down) camera.Rotate (-1.0, 0.0, 0.0, true) Endif   End   End Function Main () ' Windowed mode... Local width:Int = 640 Local height:Int = 480 Local flags:WindowFlags = WindowFlags.Center ' Full-screen mode (comment out above)... ' Local width:Int = 1920 ' Local height:Int = 1080 ' Local flags:WindowFlags = WindowFlags.Fullscreen New AppInstance New Game (AppName, width, height, flags) App.Run () End

[/crayon]

[Mark SiblyKeymaster]

Use something like entity.Matrix * vertex.position, eg:

Monkey

Local v2:Vec2f = from_camera.ProjectToViewport( Self.Matrix * v.position )

1	Local v2:Vec2f = from_camera.ProjectToViewport( Self.Matrix * v.position )

The matrix multiplication transforms the Vec3f position from one coord space (ie: local space) to another (ie: world space).

To get from world space to local space instead, use the inverse matrix, eg: -entity.Matrix * worldPos.

[DruggedBunnyParticipant]

Thanks, Mark, that looks to have done it… handy to know it was that simple!

[Mark SiblyKeymaster]

The other usefull thing to know here is how multiplying matrices has the effect of ‘chaining’ a sequence of transforms together.

So say you’ve got 2 entities, and a point in local space of one of the entities, and you want to transform it into the local space of the other entity, you can do something like -entity2.Matrix * entity1.Matrix * point.  This will transform a point from entity2’s local space to entity1’s local space. Note that matrix multiplication is not commutative (eg: matrix1*matrix2 is not the same as matrix2*matrix1) although it is associative (eg: (matrix1*matrix2)*matrix3 is the same as matrix1*(matrix2*matrix3)) and should generally be read ‘right to left’ (eg: the above first transforms point by entity1.Matrix and then by -entity2.Matrix). So by precalculating matrices like this, you can actually store a complex sequence of transforms in a singe matrix. This is what those weird sounding matrices like ‘ModelViewProjectionMatrix’ are actually doing, transforming from model space to view space to ‘clip’ space (another topic!)…

And that’s it – that’s most of what I know about 3d!

[DruggedBunnyParticipant]

Cool, thanks, have saved that for reference, will try grasp it, or as much as I need when I need it!

I have stumbled across ModelViewProjectionMatrix and the like in GLSL fragment shaders, something I’ll be dabbling in again soon, and I realised earlier that this vertex drawing is probably a good candidate for shader-ising anyway.

Got my terrain vertex drawing working for now, slow as heck (obviously), but this might actually help me narrow it down within a given range and speed up slightly.

At least I can see where the vertices are in relation to my texture, which is what I was after!

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