Native Graphic Colors

Liberty BASIC's color statement causes graphics to be drawn in with a pen of the specified color. Liberty BASIC's backcolor statement causes graphics ojects to be filled with a brush of the specified color.

Windows GDI creates colored pens with CreatePen. GDI creates brushes with CreateSolidBrush and CreateHashBrush.

GDI Brushes and Pens in Liberty BASIC

Pens and brushes can be created with GDI commands, then selected into the Device Context of a graphicbox. (See earlier lessons in this series for more on Device Contexts.) Liberty BASIC will use these pens and brushes when drawing objects such as "box", "boxfilled", "circle", "circlefilled" and so on.

CreatePen

Pens are the equivalent of Liberty BASIC's graphics "color" statement. When a pen is selected into a Device Context it is used to draw the outlines of objects, such as circles, lines, etc. Only one pen may be selected into a Device Context at a time. The selected pen is used for all drawing until another pen is selected. The default pen in a Device Context is a solid, black pen that is one pixel in width.

CreatePen has three input parameters. You must specify a style, a width and a color. All styles other than a solid pen must be one pixel wide. If a different width is specified, the pen style defaults to solid.

The pen styles are as follows:

_PS_SOLID	The pen is solid. Width MUST be one.
_PS_DASH	The pen is dashed. Width MUST be one.
_PS_DASHDOT	The pen is dotted. Width MUST be one.
_PS_DASHDOT	The pen has alternating dashes and dots. Width MUST be one.
_PS_DASHDOTDOT	The pen has alternating dashes and double dots. Width MUST be one.
_PS_NULL	The pen is invisible.

The color value is a long integer created from the desired red, green and blue values. See GDI and the Device Context for more on long color values.

    calldll #gdi32,"CreatePen",_
    style as long,_  'pen style
    width as long,_  'width in pixels
    rgbCol as long,_ 'long color value
    CreatePen as ulong 'handle to pen
    end function

SelectObject

The pen is not used until it is selected into the Device Context with SelectObject. The function returns the handle of the original object of the type and this default object can be selected back into the Device Context later.

    CallDLL #gdi32,"SelectObject",_
    hDC as uLong,_        'handle of DC
    hObj as uLong,_       'handle of object to select
    SelectObject as uLong 'returns previously selected object

DeleteObject

When an object is no longer needed, we use DeleteObject to free the memory consumed by the object. Do not attempt to delete an object that is currently selected into a Device Context. We first use SelectObject to select the default object back into the Device Context. We may then delete the created object, like so:

    CallDLL #gdi32,"DeleteObject",_
    hObj as uLong,_    'handle of object
    r As long

CreateSolidBrush

A solid brush is created with this code, which requires a long color value and returns the handle of the solid brush:

    calldll #gdi32, "CreateSolidBrush",_
    rgbCol as long,_    'long color value
    CreateSolidBrush as ulong 'returns handle of brush

Only one brush may be selected into a Device Context at one time. We do this with SelectObject* just as we did for the created pen discussed earlier. We reserve the handle of the default brush to select back into the Device Context later, just as we did for the pen.

CreateHatchBrush

A hatch brush is not a solid color; it has a cross-hatched pattern. The styles may be any of the following.

_HS_BDIAGONAL	45-degree upward left-to-right hatch
_HS_CROSS	Horizontal and vertical crosshatch
_HS_DIAGCROSS	45-degree crosshatch
_HS_FDIAGONAL	45-degree downward left-to-right hatch
_HS_HORIZONTAL	Horizontal hatch
_HS_VERTICAL	Vertical hatch

CreateHatchBrush also requires a long color value for the brush.

    calldll #gdi32, "CreateHatchBrush",_
    style as long,_ 'brush style
    rgbCol as long,_    'long color value
    CreateHatchBrush as ulong   'handle of brush

Once created, it may be selected into a Device Context in exactly the same way as the pen and solid brush discussed earlier. Like them, it must be deleted when no longer needed, in order to free memory.

GDI Drawn Objects

The examples here demonstrate the creation of pens and brushes and their use with native Liberty BASIC drawing commands. We can also draw graphics with GDI commands, using these pens and brushes. We can even draw on memory Device Contexts. This will be covered in a later lesson.

Demo

Run the code and you will see this:

nomainwin
winWide=700:winHigh=500
WindowWidth=winWide+50:WindowHeight=winHigh+50
UpperLeftX=1:UpperLeftY=1
 
graphicbox #1.g, 0,0,winWide,winHigh
open "GDI Demo" for window as #1
    #1 "trapclose [quit]"
    #1.g "down"
 
    hDC = GetDC(hwnd(#1.g))  'device context handle of graphicbox
    hPen = CreatePen(_PS_DASHDOT,1,MakeRGB(240,200,140))
    oldPen = SelectObject(hDC,hPen)
    #1.g "place 10 10; box 200 100"
 
    hBrush = CreateSolidBrush(MakeRGB(100,200,255))
    oldBrush = SelectObject(hDC,hBrush)
    #1.g "place 10 120; boxfilled 200 250"
 
    hHatch = CreateHatchBrush(_HS_CROSS,MakeRGB(200,80,170))
    hObj = SelectObject(hDC,hHatch)
    #1.g "place 10 270; boxfilled 200 420"
 
wait
 
[quit]
    re = SelectObject(hDC,oldPen)
    re = SelectObject(hDC,oldBrush)
 
    call ReleaseDC hwnd(#1.g),hDC
    call DeleteObject hPen
    close #1:end
 
function CreateSolidBrush(rgbCol)
    calldll #gdi32, "CreateSolidBrush",_
    rgbCol as long,_    'long color value
    CreateSolidBrush as ulong 'returns handle of brush
    end function
 
function CreateHatchBrush(style,rgbCol)
'_HS_BDIAGONAL 45-degree upward left-to-right hatch
'_HS_CROSS Horizontal and vertical crosshatch
'_HS_DIAGCROSS 45-degree crosshatch
'_HS_FDIAGONAL 45-degree downward left-to-right hatch
'_HS_HORIZONTAL Horizontal hatch
'_HS_VERTICAL Vertical hatch
 
    calldll #gdi32, "CreateHatchBrush",_
    style as long,_ 'brush style
    rgbCol as long,_    'long color value
    CreateHatchBrush as ulong   'handle of brush
    end function
 
function CreatePen(style,width,rgbCol)
'styles
'_PS_SOLID The pen is solid.
'_PS_DASH The pen is dashed. Width MUST be one.
'_PS_DOT The pen is dotted. Width MUST be one.
'_PS_DASHDOT The pen has alternating dashes and dots. Width MUST be one.
'_PS_DASHDOTDOT The pen has alternating dashes and double dots. Width MUST be one.
'_PS_NULL The pen is invisible.
'If width is >1 a solid pen is created.
    calldll #gdi32,"CreatePen",_
    style as long,_  'pen style
    width as long,_  'width in pixels
    rgbCol as long,_ 'long color value
    CreatePen as ulong 'handle to pen
    end function
 
function MakeRGB(red,green,blue)
    if red<0 then red=0
    if red>255 then red=255
    if green<0 then green=0
    if green>255 then green=255
    if blue<0 then blue=0
    if blue>255 then blue=255
    MakeRGB=(blue*256*256)+(green*256)+red
    end function
 
function GetDC(h)
    'get device context for window:
    calldll #user32, "GetDC",_
    h as ulong,_ 'graphicbox handle
    GetDC as ulong 'returns handle to device context
    end function
 
function SelectObject(hDC, hObj)
    CallDLL #gdi32,"SelectObject",_
    hDC as uLong,_        'handle of DC
    hObj as uLong,_       'handle of object to select
    SelectObject as uLong 'returns previously selected object
    end function
 
sub DeleteObject hObj
    CallDLL #gdi32,"DeleteObject",_
    hObj as uLong,_
    r As long
    end sub
 
sub ReleaseDC h, hdc
    calldll #user32, "ReleaseDC",_
    h as ulong,_    'window handle
    hdc as ulong,_  'device context
    ret as long
    end sub

GDI Tutorials Home

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