Using a GFX Include file

Important note: The AmiBroker 5.09.0 Beta introduced the following new GFX functions:

Status(“pxchartleft”) – returns x-coordinate of top-left corner of chart area
Status(“pxcharttop”) – returns y-coordinate of top-left corner of chart area
Status(“pxchartright”) – returns x-coordinate of bottom-right corner of chart area
Status(“pxchartbottom”) – returns y-coordinate of bottom-right corner of chart area
Status(“pxchartwidth”) – returns width chart area (right-left)
Status(“pxchartheight”) – returns width chart area (bottom-top)

Since this release appeared after this post was published these functions are not used in the examples below. This post has been left unchanged for educational purposes. For examples using the new functions please see the 5.09.0 Read Me file.

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While the post Creating GFX Chart-Overlays (v2) may have clarified a few of the more important aspects of using GFX functions, it doesn’t really give you a “quick Start” template to get started. Using a GFXInclude file can remove some of the burden of having to define pixel and charting parameters. The Include file at the bottom of this post contains most definitions as well as these common functions that you may want to call from your GFX application:

GetVisualBarIndex( ); // Returns array containing index for visible bars
gfxPlotHLineYPixelsColor ); // Plots horizontal line at level YPixels
gfxPlotVLineXPixelsColor ); // plots vertical line at level XPixels
GetYPixels); // Convert a vertical price number to the pixel equivalent
GetXPixels); // Convert a horizontal DateTime number value to the pixel equivalent

Of course you can, and should, add additional functions of your own. Here is an example of how to call the above functions to draw a GFX cross-hair cursor (Red in the capture):

gfxcrosshair.jpg

Here is the code that produced the above image:

GraphXSpace 5// See the AmiBroker help on how to init these variables
GfxSetBkModebkmode );
GfxSetOverlayModemode );
GfxSelectPencolorRed );
 
PlotC""colorBlackstyleLine ); // To define miny and maxy
#include <GFXInclude-001.afl> // Located in your default Include folder
 
// Example to draw cross-hair cursor
Yprice GetCursorYPosition(0);
XIndex SelectedValue(GetVisualBarIndex( ));
gfxPlotHLineGetYPixelsYPrice ), colorRed );
gfxPlotVLineGetXPixelsXIndex ), colorRed );

The include file listed below defines the following variables:

// pxwidth, pxheight, Miny, MinX, YRange, VisBarIndex, NumBarsVisible, pxPaneWidth, pxPaneheight, PixelsPerBar, PixelsPerPrice

You may want to copy the above comment line below the #include statement in your code to refresh your memory. You should copy the Include file to your default AmiBroker Include folder.

// GFXInclude-001.afl copy to default include folder

function gfxPlotHLineYPixelsColor )
{
    global pxwidth;
    GfxSelectPenColor ) ;
    GfxMoveTo0YPixels );
    GfxLineTopxwidthYPixels );
}
 
function gfxPlotVLineXPixelsColor )
{
    global pxheight;
    GfxSelectPenColor ) ;
    GfxMoveToXPixels);
    GfxLineToXPixelspxheight );
}
 
function GetVisualBarIndex( )
{
    lvb Status"lastvisiblebar" );
    fvb Status"firstvisiblebar" );
    bi BarIndex();
    StaticVarSet"NumberbarsVisible"Lvb fvb );
    return bi bi] - fvb;
}

function GetYPixels)
    {
    global PixelsPerPricepxTopAreaMaxY; 
    return (MaxY Y) * PixelsPerPrice pxTopArea;
    }

function GetXPixels)
    {
    global PixelsPerBarpxLeftArea;
    return PixelsPerBar pxLeftArea;
    }

_SECTION_BEGIN("GFX INITIALIZATION");
// These Parameters will change depending on screen layout/fonts
pxRightArea Param"Right Axis Area"930200); // Depends on font
pxDateArea Param"Date Axis Area"110100); // Depends on font
DateaxisOn ParamToggle"Date Axis""HIDE|SHOW");

pxLeftArea 5pxTopArea 5pxBottomArea 5; 
if ( DateaxisOn )
{
    pxBottomArea pxDateArea pxBottomArea;
    SetChartOptions2chartShowDates );
}
else
    SetChartOptions3chartShowDates );

pxwidth Status"pxwidth" );
pxheight Status"pxheight" );

// clalculate charting area width and height
Miny Status"axisminy" );
Maxy Status"axismaxy" );
YRange MaxY MinY;
VisBarIndex =  GetVisualBarIndex( );
NumBarsVisible StaticVarGet"NumberbarsVisible" );

// Calculate Pane width and height
pxPaneWidth pxwidth pxLeftArea pxRightArea;
pxPaneHeight pxHeight pxTopArea pxBottomArea;

// calculate conversion factors
PixelsPerBar     pxPaneWidth NumBarsVisible;
PixelsPerPrice pxPaneHeight YRange;
_SECTION_END();

Edited by Al Venosa.

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