--backgroud--

DESCRIPTION

layers.library/--backgroud--

 Layers library controls the display and clipping of windows on screens
 and provides means for clipped offscreen drawing. Since V52 the display
 of intuition screens can be composited enabling real alpha channel
 functionalities. This is called the Enhanced Display and is controlled
 on the intuition level. The main difference is that with composited screens
 drawing directly to the screen (as done by some legacy applications) can no
 longer work. This means operations like lasso or dragging cannot be done while
 having a LockLayers lock on the screen's LayerInfo. Instead, one should just
 use normal windows for dragging, lasso, etc. Do note that intuition APIs
 should generally be used for such purposes and therefore some functionalities
 are not exposed to the programmer in layers

IsLayerHitable

Check whether a layer can be found by WhichLayer (V52)

SYNOPSIS

    visible = IsLayerHitable( l )
    BOOL IsLayerHitable( struct Layer * );

DESCRIPTION

   Checks whether the layers hitlevel allows the layer to be found with WhichLayer
   with its current opacity value. Please see WA_HitLevel for more information

INPUTS

    layer - pointer to a Layer

RESULT

    visible - TRUE if the layer can be found

SEE ALSO

• WA_Opacity
• WA_HitLevel

IsLayerVisible

Check whether a layer is visible or hidden (V52)

SYNOPSIS

    visible = IsLayerVisible( l )
    BOOL IsLayerVisible( struct Layer * );

DESCRIPTION

   Checks whether a layer is visible, that is: whether it is not hidden or
   has a non-zero opacity. It does not check whether the layer is totally
   covered by other layers

INPUTS

    layer - pointer to a Layer

RESULT

    visible - TRUE if the layer is visible

SEE ALSO

• WA_Opacity

IsVisibleInLayer

Check whether a given rectangle is not fully clipped away (V52)

SYNOPSIS

    visible = IsVisibleInLayer( l, x0, y0, x1, y1 )
    BOOL IsVisibleInLayer( struct Layer *, LONG, LONG, LONG, LONG );

DESCRIPTION

   Checks whether a given rectangle is not fully clipped away using the layer's
   current clipping rectangle. On Enhanced Display screens this will only check
   whether the rectangle isn't outside the layer's custom shape clip area

INPUTS

    layer - pointer to a Layer
   x0 - y1 - a rectangle in coordinates relative to the layer

RESULT

    visible - TRUE if any portion of the rectangle is in the visible area

LockLayerUpdates

Ensure a flickerless redraw with multiple draw ops (V52)

SYNOPSIS

    LockLayerUpdates( l )
    void LockLayerUpdates( struct Layer * );

DESCRIPTION

   On Enhanced Display screens this call ensures that multiple drawing operations
   will not cause flicker on screen - that is, the screen contents will not be
   updated inbetween your drawing calls.

   Do note that this call may need to access multiple layers, therefore you must
   either not hold any layer locks in the LayerInfo the layer belongs to, or call
   LockLayerInfo() before using this function.

   Do note that there is no need to call this function when the application has
   just called BeginRefresh() / BeginUpdate().

   UnlockLayerUpdates MUST be called as many times as LockLayerUpdates was called.
   Do not hold the lock longer than it is necessary - depending on the
   implementation it may lock the updates of the whole screen. As with the other
   layers locking functions, high level system calls are forbidden, especially
   intutition.library's window operations

INPUTS

    layer - pointer to a Layer

SEE ALSO

• UnlockLayerUpdates

RenderLayerInfo

Render a portion of a LayerInfo in a buffer (V52)

SYNOPSIS

    success = RenderLayerInfoTagList( li, tags )
   BOOL RenderLayerInfoTagList( struct LayerInfo *, struct TagItem *);
   BOOL RenderLayerInfoTags( struct LayerInfo *, Tag tag1, ...);

DESCRIPTION

   Renders an Enhanced Display screen LayerInfo's contents in a buffer

INPUTS

    layer - pointer to a Layer
   tags - pointer to TagItem list

   Currently defined tags are:

       LR_Destination_RastPort
       LR_Destination_BitMap
       LR_Destination_Bounds
       LR_LayerInfo_Bounds
       LR_Erase
       LR_RenderList
       LR_IgnoreList

   Please see the graphics/layers.h include file for their descriptions

RESULT

    success - TRUE if anything was rendered at all

SEE ALSO

• graphics/layers.h

UnlockLayerUpdates

Removes the LockLayerUpdates lock (V52)

SYNOPSIS

    UnlockLayerUpdates( l )
    void UnlockLayerUpdates( struct Layer * );

DESCRIPTION

   Unlocks a layer previously locked with LockLayerUpdates

INPUTS

    layer - pointer to a Layer

SEE ALSO

• LockLayerUpdates

WhichLayerBehindLayer

Returns a layer from a point, ignoring one layer (V52)

SYNOPSIS

    layer = WhichLayerBehindLayer( l, x, y )
    struct Layer * WhichLayerBehindLayer( struct Layer *, LONG, LONG);

DESCRIPTION

   Scans the LayerInfo of the passed in layer starting from the layer directly
   below the passed in layer and returns the first layer overlapping the given
   coordinates.

   Do note that you should call this function inside a LockLayerInfo() or
   LockLayers() if you wish to use the returned pointer for any other means
   than simple pointer comparison. In other words, if you wish to peek the
   returned structure or call any layers functions on it, obtain the lock first.

   This function makes it easy to implement window-based dragging effects

INPUTS

    layer - pointer to a Layer
   x, y - LayerInfo relative coordinates

RESULT

    layer - pointer to struct Layer or NULL

SEE ALSO

• WhichLayer