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# How To ... Develop a Bitmap Painting Tool - Unwrap UV Coordinates

How To > Develop a Bitmap Painting Tool- Unwrap UV Coordinates

In this exciting step of the Bitmap Painting tool development, we will add the option to generate a graphical representation of the UV coordinates of an object inside the painting tool and assign automatically as diffuse map to the scene object.

NATURAL LANGUAGE
We will add a local variable to store the mesh object to work with.
We will add a new filter function to select only mesh objects.
We will add a new pickbutton to the UI to select an object to work with which will use the filter function.
We will add an option to the Edit menu to acquire the texture coordinates
We will add a new function to read UV coordinates from a selected mesh and draw strokes in the painting based on the vertex positions in texture space
We will define a default temp. file name for the painting and will optionally save it after each stroke
We will assign the temp. disk copy of the bitmap to the diffuse channel of the picked object.
We will add a new checkbox to the User Interface to enable and disable autosaving. When enabled, the bitmap will update in realtime as we paint in our tool!

SCRIPT:
    macroScript MicroPaint category: "HowTo"
    (
    global MicroPaint_CanvasRollout
    try (destroyDialog MicroPaint_CanvasRollout) catch()
    local isErasing = isDrawing = false
    local bitmapX = bitmapY = 512
    local bitmapx_1 = bitmapx-1
    local bitmapy_1 = bitmapy-1
    local temp_bitmap_filename = (getDir #preview +"/microPaint_temp.bmp")
    local theCanvasBitmap = bitmap bitmapX bitmapY color:white filename:temp_bitmap_filename
    local theBackgroundBitmap = bitmap bitmapX bitmapY color:white
    local currentPos = lastPos = [0,0]

    local theChannel = 1
    local theObj = undefined

    rcMenu CanvasMenu
    (
      subMenu "File"
      (
        menuItem new_menu "New"
        menuItem open_menu "Open..."
        menuItem save_ as "Save As..."
        separator file_menu_1
        menuItem quit_tool "Quit"
      )
      subMenu "Edit"
      (
        menuItem commit_menu "Commit Changes"
        separator edit_menu_1
        menuItem uv_menu "Get UV Coordinates..."
      )
      on commit_menu picked do copy theCanvasBitmap theBackgroundBitmap
      on uv_menu picked do MicroPaint_CanvasRollout.unwrapTexture()

      subMenu "Help"
      (
        menuItem about_tool "About MicroPaint..."
      )

      on new_menu picked do
      (
        theBackgroundBitmap = theCanvasBitmap = bitmap bitmapX bitmapY color:MicroPaint_CanvasRollout.paperColor.color filename:temp_bitmap_filename
        MicroPaint_CanvasRollout.theCanvas.bitmap = theCanvasBitmap
      )

      on open_menu picked do
      (
        theOpenBitmap= selectBitmap()
        if theOpenBitmap != undefined do
        (
          copy theOpenBitmap theCanvasBitmap
          copy theOpenBitmap theBackgroundBitmap
          close theOpenBitmap
          MicroPaint_CanvasRollout.theCanvas.bitmap = theCanvasBitmap
        )
      )

      on save_as picked do
      (
        theSaveName = getSaveFileName types:"BMP (*.bmp)|*.bmp|Targa (*.tga)|*.tga|JPEG (*.jpg)|*.jpg"
        if theSaveName != undefined do
        (
          theCanvasBitmap.filename = theSaveName
          save theCanvasBitmap
          theCanvasBitmap.filename = temp_bitmap_filename
        )
      )
      on about_tool picked do messagebox "MicroPaint\nMAXScript Tutorial" title:"About..."
      on quit_tool picked do destroyDialog MicroPaint_CanvasRollout
    )

    fn mesh_filter obj = superclassof obj == GeometryClass and classof obj != TargetObject

    rollout MicroPaint_CanvasRollout "MicroPaint"
    (
      bitmap theCanvas pos:[0,0] width:bitmapX height:bitmapY bitmap:theCanvasBitmap
      colorpicker inkColor height:16 modal:false color:black across:6
      colorpicker paperColor height:16 modal:false color:white
      checkbutton autoSave "AutoSave" width:70
      checkbutton airBrush "AirBrush" width:70
      spinner AirBrushSpeed "Speed" range:[0.1,50,10] fieldwidth:30
      spinner BrushSize "Size" range:[1,50,1] type:#integer fieldwidth:40
      listbox BrushShape items:#("Circle","Box","Circle Smooth") pos:[bitmapX+5,0] width:90

      --NEW PICK BUTTON AND HANDLER:
      pickbutton pickMesh "Pick Mesh" width:90 height:30 pos:[bitmapX+5,140] filter:mesh_filter autodisplay:true

      on pickMesh picked obj do
      (
        if obj != undefined do
        (
          theObj = Obj
          try
          (
            copy theObj.material.diffusemap.bitmap theCanvasBitmap
            copy theObj.material.diffusemap.bitmap theBackgroundBitmap
            theCanvas.bitmap = theCanvasBitmap
          )catch()
        )
      )
      --END NEW PICK BUTTON AND HANDLER

      fn paintBrush pos =
      (
        if isErasing then
          thePaintColor = (getPixels theBackgroundBitmap pos 1)[1]
        else
          thePaintColor = inkColor.color
        if thePaintColor == undefined then thePaintColor = white

        case BrushShape.selection of
        (
          1: (
            if distance pos currentPos <= BrushSize.value/2 do
              setPixels theCanvasBitmap pos #(thePaintColor)
            )
          2: setPixels theCanvasBitmap pos #(thePaintColor)
          3: (
            theFactor = (distance pos currentPos) / (BrushSize.value/2.0)
            if theFactor <= 1.0 do
            (
              theFactor = sin ( 90.0 * theFactor)
              thePixels = getPixels theCanvasBitmap pos 1
              if thePixels[1] != undefined do
              (
                thePixels[1] = (thePixels[1] * theFactor) + (thePaintColor * (1.0 - theFactor))
                setPixels theCanvasBitmap pos thePixels
              )
            )
          )--end case 3
        )--end case
      )--end fn

      fn drawStroke lastPos pos drawIt: =
      (
        currentPos = lastPos
        deltaX = pos.x - lastPos.x
        deltaY = pos.y - lastPos.y
        maxSteps = amax #(abs(deltaX),abs(deltaY))
        deltaStepX = deltaX / maxSteps
        deltaStepY = deltaY / maxSteps
        for i = 0 to maxSteps do
        (
          if airBrush.checked then
            for b = 1 to (BrushSize.value / AirBrushSpeed.value) do
              paintBrush (currentPos + (random [-BrushSize.value/2,-BrushSize.value/2] [BrushSize.value/2,BrushSize.value/2] ))
          else
            for b = -BrushSize.value/2 to BrushSize.value/2 do
              for c = -BrushSize.value/2 to BrushSize.value/2 do
                paintBrush (currentPos + [c,b])
          currentPos += [deltaStepX, deltaStepY]
        )
        if drawIt== true or drawIt == unsupplied do theCanvas.bitmap = theCanvasBitmap
      )

      --NEW UNWRAP TEXTURE FUNCTION STARTS HERE
      fn unwrapTexture =
      (
        if theObj != undefined then
        (
          theMesh = snapshotAsMesh theObj
          if meshop.getMapSupport theMesh theChannel do
          (
            faceCount = meshop.getNumMapFaces theMesh theChannel
            for f = 1tofaceCount do
            (
              theFace = meshop.getMapFace theMesh theChannel f
              vert1= meshop.getMapVert theMesh theChannel theFace.x
              vert2= meshop.getMapVert theMesh theChannel theFace.y
              vert3= meshop.getMapVert theMesh theChannel theFace.z
              drawStroke [vert1.x * bitmapx_1, bitmapy_1 - vert1.y * bitmapy_1] [vert2.x * bitmapx_1, bitmapy_1 - vert2.y * bitmapy_1] drawIt:false
              drawStroke [vert1.x * bitmapx_1, bitmapy_1 - vert1.y * bitmapy_1] [vert3.x * bitmapx_1, bitmapy_1 - vert3.y * bitmapy_1] drawIt:false
              drawStroke [vert3.x * bitmapx_1, bitmapy_1 - vert3.y * bitmapy_1] [vert2.x * bitmapx, bitmapy_1 - vert2.y * bitmapy_1] drawIt:false
            )
          )
          theCanvas.bitmap = theCanvasBitmap
          save theCanvasBitmap
          if theObj.material == undefined do theObj.material = Standard()
          if theObj.material.diffusemap == undefined do
            theObj.material.diffusemap = bitmapTexture filename:temp_bitmap_filename
          showTextureMap theObj.material true
          autoSave.checked = true
        )
      )
      --NEW UNWRAP TEXTURE FUNCTION ENDS HERE

      on autoSave changed state do if state do save theCanvasBitmap

      on MicroPaint_CanvasRollout lbuttondown pos do
      (
        lastPos = pos
        isDrawing = true
        isErasing = false
        drawStroke lastPos pos
      )
      on MicroPaint_CanvasRollout rbuttondown pos do
      (
        lastPos = pos
        isErasing = isDrawing = true
        drawStroke lastPos pos
      )
      on MicroPaint_CanvasRollout lbuttonup pos do
      (
        isErasing = isDrawing = false
        if autoSave.checked do save theCanvasBitmap
      )
      on MicroPaint_CanvasRollout rbuttonup pos do
      (
        isErasing = isDrawing = false
        if autoSave.checked do save theCanvasBitmap
      )

      on MicroPaint_CanvasRollout mousemove pos do
      (
        if isDrawing do drawStroke lastPos pos
        lastPos = pos
      )
    )
    createDialog MicroPaint_CanvasRollout (bitmapx+100) (bitmapy+30) menu:CanvasMenu
    MicroPaint_CanvasRollout.theCanvas.bitmap = theBackgroundBitmap
    )

## Step-By-Step

    --Code in italic has not changes since the previous version! macroScript MicroPaint category:"HowTo"
    (
    global MicroPaint_CanvasRollout
    try(destroyDialog MicroPaint_CanvasRollout)catch()
    local isErasing = isDrawing = false
    local bitmapX = bitmapY = 512

    local bitmapx_1 = bitmapx-1 local bitmapy_1 = bitmapy-1

In order to calculate the position of the UV coordinates inside the bitmap, we have to count the pixels as the size of the bitmap minus one (for example, 0 to 511 and not 1 to 512). To make out life easier, we define two variables to store these corrected values.

    local temp_bitmap_filename = (getDir #preview +"/microPaint_temp.tga") local theCanvasBitmap = bitmap bitmapX bitmapY color:white filename:temp_bitmap_filename

In order to be able to save the current painting to a temporary file on disk, we have to define a file name and assign it to the bitmap. The file name is stored in a local variable which will be used in other parts of the script to access it. TGA appears to be faster to save than BMP for example, but you can save to any format you want.

    local theBackgroundBitmap = bitmap bitmapX bitmapY color:white
    local currentPos = lastPos = [0,0] localtheChannel = 1

This is the map channel to read from. You could add a User Interface spinner to control its value... For now, we will work with channel 1 only.

    local theObj = undefined

This variable will store the mesh object to access the UV coordinates from.

    rcMenu CanvasMenu
    (
    subMenu "File"
    (
    menuItem new_menu "New"
    menuItem open_menu "Open..."
    menuItem save_as "Save As..."
    separator file_menu_1
    menuItem quit_tool "Quit"
    )
    subMenu "Edit"
    (
    menuItem commit_menu "Commit Changes"

    separator edit_menu_1 menuItem uv_menu "Get UV Coordinates..." )

We add a new menu item which will be used to acquire texture coordinates from a scene object.

    on commit_menu picked do copy theCanvasBitmap theBackgroundBitmap on uv_menu picked do MicroPaint_CanvasRollout.unwrapTexture()

If the user picked the menu item, we call a new function which will be defined inside the rollout. (see below)

    subMenu "Help"
    (
    menuItem about_tool "About MicroPaint..."
    )

    on new_menu picked do
    (
    theBackgroundBitmap = theCanvasBitmap = bitmap bitmapX bitmapY color:MicroPaint_CanvasRollout.paperColor.color filename:temp_bitmap_filename
    MicroPaint_CanvasRollout.theCanvas.bitmap = theCanvasBitmap
    )

    on open_menu picked do
    (
    theOpenBitmap= selectBitmap()
    if theOpenBitmap != undefined do
    (
    copy theOpenBitmap theCanvasBitmap
    copy theOpenBitmap theBackgroundBitmap
    close theOpenBitmap
    MicroPaint_CanvasRollout.theCanvas.bitmap = theCanvasBitmap
    )
    )

    on save_as picked do
    (
    theSaveName = getSaveFileName types:"BMP (*.bmp)|*.bmp|Targa (*.tga)|*.tga|JPEG (*.jpg)|*.jpg"
    if theSaveName != undefined do
    (
    theCanvasBitmap.filename = theSaveName
    save theCanvasBitmap theCanvasBitmap.filename = temp_bitmap_filename

After saving to a new file name, set back the filename to the temporary location, otherwise autosaving would start writing into the new file and we don't want this to happen!

    )
    )
    on about_tool picked do messagebox "MicroPaint\nMAXScript Tutorial" title:"About..."
    on quit_tool picked do destroyDialog MicroPaint_CanvasRollout
    )

    fn mesh_filter obj = superclassof obj == GeometryClass and classof obj != TargetObject

This function allows us to pick only geometry objects except target objects. It will be used as a filter function by a new pickbutton User Interface control.

    rollout MicroPaint_CanvasRollout "MicroPaint" ( bitmap theCanvas pos:[0,0] width:bitmapX height:bitmapY bitmap:theCanvasBitmap

    colorpicker inkColor height:16 modal:false color:black across:6

To accommodate the new autoSave option, we increase the across parameter to 6.

    colorpicker paperColor height:16 modal:false color:white

    checkbutton autoSave "AutoSave" width:70

This new checkbutton will control whether the painting is constantly saved to disk after each stroke.

    checkbutton airBrush "AirBrush" width:70
    spinner AirBrushSpeed "Speed" range:[0.1,50,10] fieldwidth:30 spinner BrushSize "Size" range:[1,50,1] type:#integer fieldwidth:40

The default brush size is now 1. This is to avoid drawing a texture unwrapping with a thickness of 10 which can be very slow...

    listbox BrushShape items:#("Circle", "Box", "Circle Smooth") pos:[bitmapX+5,0] width:90

    pickbutton pickMesh "Pick Mesh" width:90 height:30 pos:[bitmapX+5,140] filter:mesh_filter autodisplay:true

This pickbutton will be used to select the scene object to unwrap the texture coordinates. It uses the new optional keyword autoDisplay added to 3ds Max 7. When set to true, it will display the name of the picked object on the button automatically. In 3ds Max 6 and earlier, the option will be ignored, but the script will still function correctly!

Pickbutton

    on pickMesh picked obj do (

This is the event handler of the pickbutton. If the user picked an object, it will be passed to the handler in the obj variable.

    if obj != undefined do (

If the obj variable contains a valid object (in other words, the user did not cancel the picking), then

    theObj = Obj

we first assign the picked object to our new variable which will store the pick during the painting session.

    try ( copy theObj.material.diffusemap.bitmap theCanvasBitmap copy theObj.material.diffusemap.bitmap theBackgroundBitmap theCanvas.bitmap = theCanvasBitmap

Then we try to read the diffusemap bitmap of the object and copy it into the canvas and background bitmaps of the painting tool, then assign it to the UI.

If there is no bitmap there, the error will be trapped and nothing will happen.

    )catch()  ) )

    fn paintBrush pos =
    (
    if isErasing then
    thePaintColor = (getPixels theBackgroundBitmap pos 1)[1]
    else
    thePaintColor = inkColor.color
    if thePaintColor == undefined then thePaintColor = white

    case BrushShape.selection of
    (
    1: (
    if distance pos currentPos <= BrushSize.value/2 do
    setPixels theCanvasBitmap pos #(thePaintColor)
    )
    2: setPixels theCanvasBitmap pos #(thePaintColor)
    3: (
    theFactor = (distance pos currentPos) / (BrushSize.value/2.0)
    if theFactor <= 1.0 do
    (
    theFactor = sin ( 90.0 * theFactor)
    thePixels = getPixels theCanvasBitmap pos 1
    if thePixels[1] != undefined do
    (
    thePixels[1] = (thePixels[1] * theFactor) + (thePaintColor * (1.0 - theFactor))
    setPixels theCanvasBitmap pos thePixels
    )
    )
    )--end case 3
    )--end case
    )--end fn
      fn drawStroke lastPos pos drawIt: = (

We add a new optional keyword to the drawStroke function. If it is set to false, the stroke will be drawn but the bitmap will not be updated in the rollout. If it is true or not supplied, the bitmap will be updated after the stroke. This is to allow for faster drawing of the unwrapped texture without updating the view after each texture face!

    currentPos = lastPos
    deltaX = pos.x - lastPos.x
    deltaY = pos.y - lastPos.y
    maxSteps = amax #(abs(deltaX),abs(deltaY))
    deltaStepX = deltaX / maxSteps
    deltaStepY = deltaY / maxSteps
    for i = 0 to maxSteps do
    (
    if airBrush.checked then
    for b = 1 to (BrushSize.value / AirBrushSpeed.value) do
    paintBrush (currentPos + (random [-BrushSize.value/2,-BrushSize.value/2] [BrushSize.value/2,BrushSize.value/2] ))
    else
    for b = -BrushSize.value/2 to BrushSize.value/2 do
    for c = -BrushSize.value/2 to BrushSize.value/2 do
    paintBrush (currentPos + [c,b])
    currentPos += [deltaStepX, deltaStepY]
    ) if drawIt== true or drawIt == unsupplied do theCanvas.bitmap = theCanvasBitmap

If the new switch is set to true or not set at all, we update the display as before, otherwise the update is skipped!

    ) fn unwrapTexture = (

This is the new function which performs the selection of an object, the unwrapping of the texture coordinates and the material/texture assignment.

    if theObj != undefined then (

If the user clicked a valid object...

    theMesh =snapshotAsMeshtheObj

...we extract the mesh from the top of its stack.

    if meshop.getMapSupport theMesh theChannel do (

If the selected object supports the specified channel,

    faceCount = meshop.getNumMapFaces theMesh theChannel

we read the number of texture faces in that channel...

    for f = 1 to faceCount do (

...and repeat the following code for every face found in the mesh:

    theFace = meshop.getMapFace theMesh theChannel f

This is the map face definition. It returns a Point3 value where .x .y and .z are indices pointing at the texture vertices the face is using.

    vert1= meshop.getMapVert theMesh theChannel theFace.x vert2= meshop.getMapVert theMesh theChannel theFace.y vert3= meshop.getMapVert theMesh theChannel theFace.z

Using this data, we read the 3 vertices of the face. Each one is a Point3 value containing the actual U, V and W values. We will draw only the UV and discard the W though.

    drawStroke [vert1.x * bitmapx_1, bitmapy_1- vert1.y * bitmapy_1] [vert2.x * bitmapx_1, bitmapy_1- vert2.y * bitmapy_1] drawIt:false

We call the drawStroke function using the first and second texture vertex coordinates multiplied by the size of the bitmap. The flag drawIt is set to false to speed up the generation of the image. If you would change it to true, you could watch the function drawing interactively in the image, but this could take a very long time.

The calculation of the coordinates is based on the fact that the lower left corner of the UV space has coordinates 0,0 and the upper right has coordinates 1,1.

The bitmap on the other hand has its UPPER left corner as 0,0 and its lower right corner as bitmapx-1,bitmapy-1 (511,511 in our example).

So in order to convert the UV coordinates in pixel coordinates, we multiply the width resp. height of the bitmap by the U resp. V value, and turn the vertical result upside-down by subtracting from the height.

    drawStroke [vert1.x * bitmapx_1, bitmapy_1- vert1.y * bitmapy_1] [vert3.x * bitmapx_1, bitmapy_1- vert3.y * bitmapy_1] drawIt:false drawStroke [vert3.x * bitmapx_1, bitmapy_1- vert3.y * bitmapy_1] [vert2.x * bitmapx_1, bitmapy_1- vert2.y * bitmapy_1] drawIt:false

We call the drawStroke function for the other two pairs of vertices, thus drawing all edges of the face.

    ) )  theCanvas.bitmap = theCanvasBitmap

Now we can update the rollout bitmap to show the result.

    save theCanvasBitmap

We can also save the bitmap to its temporary location.

    if theObj.material == undefined do theObj.material = Standard()

If the selected object has no material, we assign a new material.

    try (if theObj.material.diffusemap == undefined do theObj.material.diffusemap = bitmapTexture filename:temp_bitmap_filename

If the selected object's diffusemap is not defined yet, we try to assign a new texture map pointing at the temporary copy of our painting. If the object does not have a standard material assigned, trying to access the diffusemap channel will cause an error which will be prevented by the try()catch() context.

    showTextureMap theObj.material true

We press the Show Map In Viewport of the material at object level. If the texture assignment was successful, the bitmap should be shown in the viewport.

    autoSave.checked = true

If everything went ok, we can also turn the new autosave option on to force the bitmap to update on the selected object as you paint...

    )catch() ) ) on autoSave changed state do if state do save theCanvasBitmap

If the user checked the new checkbutton, the bitmap will be saved to its temporary location immediately.

    on MicroPaint_CanvasRollout lbuttondown pos do
    (
    lastPos = pos
    isDrawing = true
    isErasing = false
    drawStroke lastPos pos
    )
    on MicroPaint_CanvasRollout rbuttondown pos do
    (
    lastPos = pos
    isErasing = isDrawing = true
    drawStroke lastPos pos
    )
    on MicroPaint_CanvasRollout lbuttonup pos do
    (
    isErasing = isDrawing = false if autoSave.checked do save theCanvasBitmap

If the new checkbutton is pressed, the bitmap will be saved to its temporary location after each stroke.

    )
    on MicroPaint_CanvasRollout rbuttonup pos do
    (
    isErasing = isDrawing = false

    if autoSave.checked do save theCanvasBitmap

If the new checkbutton is pressed, the bitmap will be saved to its temporary location after each erase stroke.

     )

    on MicroPaint_CanvasRollout mousemove pos do
    (
    if isDrawing do drawStroke lastPos pos
    lastPos = pos
    )
    )
    createDialog MicroPaint_CanvasRollout (bitmapx+100) (bitmapy+30) menu:CanvasMenu
    MicroPaint_CanvasRollout.theCanvas.bitmap = theBackgroundBitmap
    )

RESULT:

In this example, Unwrap UVW modifier was applied to a teapot and the Flatten function was used to create new texture coordinates.

Then the object was selected in MicroPaint and the texture coordinates were drawn using the Circular Smooth brush with size 5, Airbrush turned on and Airbrush Speed set to 1.0.

This is the teapot as seen in the viewport:

Now you can start painting on top of the UV coordinates using all available brushes - as long as the AutoSave button is checked, all your strokes should update in the viewports:

Previous Tutorial:

How To ... Develop a Bitmap Painting Tool - Erase Changes

Next Tutorial:

How To ... Develop a Bitmap Painting Tool - 3D Painting

#### See Also

- "How To" Tutorials Index Page