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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/xml/corelib/fpg_base.xml | 71 |
1 files changed, 68 insertions, 3 deletions
diff --git a/docs/xml/corelib/fpg_base.xml b/docs/xml/corelib/fpg_base.xml index 3a2600b8..ccb599d5 100644 --- a/docs/xml/corelib/fpg_base.xml +++ b/docs/xml/corelib/fpg_base.xml @@ -2678,10 +2678,75 @@ it is shown for the first time.</short> </element> <!-- object Visibility: default --> <element name="TfpgRect"> - <short>A rectangle structure used throughout fpGUI.</short> - <descr>Note that this structure is not a class, so static allocations are + <short>A graphical (pixel based) rectangle structure used throughout fpGUI.</short> + <descr><p>Note that this structure is not a class, so static allocations are allowed. This makes it much easier to use in Widgets and in fpGUI internal -messages. +messages.</p> +<p> +Think of the pixel screen/grid like the grid of a spreadsheet (or as a magnified look of the top corner of your screen). +</p> +<pre>. + 0 1 + +---+---+--- +0 | x | | + +---+---+--- +1 | | | + +---+---+--- +2 | | | + +---+---+--- + | | | +</pre> +<p> +x is at (0,0). A pixel is always 1x1, you don't get smaller (we are not using sub-pixels like on LCD screens, because they don't apply to all screens). +</p> +<p> +So with that example, Width = 1 pixel and Height = 1 pixel. In the case of +Classes.Bounds() the Right and Bottom values are (1,1) which looking at the +above image will be wrong, the pixel only covers one block, so in a screen/pixel +environment, Right, Bottom is also (0,0), the same as Top/Left. This is what +TfpgRect.Right and TfpgRect.Bottom will report. +</p> +<pre>. + 0 1 + +---+---+--- +0 | x | x | + +---+---+--- +1 | x | x | + +---+---+--- +2 | | | + +---+---+--- + | | | +</pre> +<p> +In this example we have a rectangle. Top/Left = (0,0) and Bottom/Right = (1,1). +This means Width = 2 pixels and Height = 2 pixels. Clearly visible in the image +above. +</p> +<p> +But if we call Classes.Bounds(0,0,2,2) it reports Bottom/Right as (2,2) which +is wrong (again looking at the image above as reference). This is my point. +Bounds() cannot be used in this case in a graphical environment. +</p> +<p> +The reason I don't use a grid layout as shown below, is +because if the mouse is over the rectangle containing x, the OS (graphics system) reports its +position as (0,0). You don't have to have the mouse pointer over the intersecting +lines at (0,0) as indicated in the image below. The whole square containing +the x is referenced as (0,0), hence the grid layout as show in the images above, +and what fpGUI uses. The same grid layout as used in TfpgStringGrid or any +Spreadsheet program etc. +</p> +<pre>. + 0 1 +0 +---+---+--- + | x | | +1 +---+---+--- + | | | +2 +---+---+--- + | | | +3 +---+---+--- + | | | +</pre> </descr> <errors/> <seealso/> |