StringheightWithGetPixel

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JanetTerra JanetTerra Aug 26, 2010

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Stringheight for Liberty BASIC


Stringwidth? is the Liberty BASIC command for obtaining the width in pixels of any given character or chain of characters. Stringwidth? calculates this measurement based upon the current font in use. 
 Open "The Stringwidth? Command" for Graphics as #g 
 #g, #g "Trapclose XbyTrap" 
 char$ = "X" 
 #g, #g "Down; Place 20 50" 
 #g, #g "Font Times_New_Roman 14" 
 #g, #g "Stringwidth? char$ PixelWidth" 
 #g, #g "\The width of ";char$;" is ";PixelWidth;" pixels." 
 #g, #g "Font Courier_New 36" 
 #g, #g "Stringwidth? char$ PixelWidth" 
 #g, #g "\\The width of ";char$;" is ";PixelWidth;" pixels." 
 #g, #g "Flush" 
 Wait 
 
 Sub XbyTrap handle$ 
 Close #g 
 End 
 End Sub

Calculating Stringheight with Posxy

Unfortunately, there is no native Stringheight? function. A simple way to determine the height of a font is to use the posxy xVar yVar command. The posxy function returns the position of the graphic pen. Define the font, position the pen, draw text, get the new y position. The difference between the two y positions is the height of the font. 
 Open "Calculating Stringheight with Posxy" for Graphics as #g 
 #g, #g "Trapclose XbyTrap" 
 Char$ = "X" 
 #g, #g "Down; Place 20 50" 
 
 ' Select a font 
 #g, #g "Font Times_New_Roman 14" 
 
 ' Get the pen position before drawing the text 
 #g, #g "Posxy x1Var y1Var" 
 
 ' Draw the text 
 #g, #g "\";Char$ 
 
 ' Get the pen position after drawing the text 
 #g, #g "Posxy x2Var y2Var" 
 
 ' Subtract to determine Stringheight 
 Stringheight = y2Var - y1Var 
 
 ' Show the value of Stringheight 
 #g, #g "\The height of ";Char$;" is ";Stringheight;" pixels." 
 
 ' Select another font 
 #g, #g "Font Courier_New 36" 
 
 ' Create a linefeed 
 #g, #g "\" 
 
 ' Get the pen position before drawing the text 
 #g, #g "Posxy x1Var y1Var" 
 
 ' Draw the second text 
 #g, #g "\";Char$ 
 
 ' Get the pen position after drawing the text 
 #g, #g "Posxy x2Var y2Var" 
 
 ' Subtract to determine Stringheight 
 Stringheight = y2Var - y1Var 
 
 #g, #g "\The height of ";Char$;" is ";Stringheight;" pixels." 
 
 #g, #g "Flush" 
 Wait 
 
 Sub XbyTrap handle$ 
 Close #g 
 End 
 End Sub
This Stringheight method does not require the text to be drawn, neither does the text have to be visible. Here is the same method using a 1 x 1 graphicbox that is set offscreen, thus invisible to the user. 
 Graphicbox #main.g, -10, -10, 1, 1 
 Statictext #main.t, "Font Dimensions", 20, 50, 250, 100 
 Open "Calculating Stringheight with Posxy" for Window as #main 
 #main, #main "Trapclose XbyTrap" 
 #main, #main "Font Verdana 12 Bold" 
 Char$ = "X" 
 #main.g, #main.g "Down; Place 20 50" 
 
 ' Select a font 
 #main.g, #main.g "Font Times_New_Roman 14" 
 
 ' Calculate Stringwidth using the native Stringwidth? function 
 #main.g, #main.g "Stringwidth? Char$ Stringwidth" 
 
 ' Get the pen position before drawing the text 
 #main.g, #main.g "Posxy x1Var y1Var" 
 
 ' Draw the text 
 #main.g, "\";Char$ 
 
 ' Get the pen position after drawing the text 
 #main.g, #main.g "Posxy x2Var y2Var" 
 
 ' Subtract to determine Stringheight 
 Stringheight = y2Var - y1Var 
 
 ' Show the value of Stringwidth and Stringheight 
 FontDimensions$ = "The dimensions of " ;Char$;" are " + _ 
 Str$(Stringwidth);" pixels wide and ";Str$(Stringheight) + _ 
 " pixels high." 
 #main.t, #main.t FontDimensions$ 
 
 Wait 
 
 Sub XbyTrap handle$ 
 Close #main 
 End 
 End Sub

Disadvantages of Using Posxy to Calculate Stringheight

Posxy will not return the exact position of the drawn text. It only returns the number of vertical (y) pixels advanced to for beginning the next line. The font space includes not just the font, but padding above, below, to the left, and to the right, of the character itself. The y1Var is the lower position of the drawn font, above the lower padding of the font space. 
 Open "Calculating Stringheight with Posxy" for Graphics as #g 
 #g, #g "Trapclose XbyTrap" 
 Char$ = "X" 
 #g, #g "Down; Place 20 50" 
 #g, #g "Color Black; Backcolor Cyan" 
 #g, #g "Font Times_New_Roman 14" 
 #g, #g "Posxy x1Var y1Var" 
 #g, #g "\";Char$ 
 #g, #g "Posxy x2Var y2Var" 
 Stringheight = y2Var - y1Var 
 
 #g, #g "Color Red" 
 ' Draw a red line at y1Var 
 #g, #g "Line 0 ";y1Var;" 100 ";y1Var 
 
 ' Draw a red line at y2Var 
 #g, #g "Line 0 ";y2Var;" 100 ";y2Var 
 #g, #g "Flush" 
 Wait 
 
 Sub XbyTrap handle$ 
 Close #g 
 End 
 End Sub

Stringheight Wrapped in a Function

Still, if all that is needed is the vertical height of the font space, a simple custom function using an offscreen graphicbox is quick and easy. 
 Nomainwin 
 WindowWidth = 800 
 WindowHeight = 600 
 UpperLeftX = Int((DisplayWidth - WindowWidth) /2) 
 UpperLeftY = Int((DisplayHeight - WindowHeight) /2) 
 Graphicbox #main.h, -10, -10, 1, 1 ' Hidden graphicbox 
 Graphicbox #main.g, 0, 0, 800, 600 ' Visible graphicbox 
 Open "Calculating Stringheight with Posxy" for Window as #main 
 #main, #main "Trapclose XbyTrap" 
 CurrentFont$ = "Verdana 32 Bold" 
 #main.g, #main.g "Font ";CurrentFont$ 
 Stringheight = Stringheight(CurrentFont$) 
 #main.g, #main.g "Down; Place 20 50" 
 For i = 1 to 10 
 #main.g, #main.g "\Line ";i 
 Next i 
 #main.g, #main.g "Color Red" 
 yPos = 55 
 For i = 1 to 10 
 For x = 20 to 250 Step 5 
 #main.g, #main.g "Place ";x;" ";yPos 
 #main.g, #main.g "Circle 4" 
 Next x 
 yPos = yPos + Stringheight 
 Next i 
 #main.g, "Flush" 
 
 Wait 
 
 Sub XbyTrap handle$ 
 Close #main 
 End 
 End Sub 
 
 Function Stringheight(CurrentFont$) 
 #main.h, #main.h "Cls" 
 #main.h, #main.h "Font ";CurrentFont$ 
 #main.h, #main.h "Place 20 500" 
 #main.h, #main.h "Posxy x1Var y1Var" 
 #main.h, #main.h "\X" 
 #main.h, #main.h "Posxy x2Var y2Var" 
 Stringheight = y2Var - y1Var 
 End Function

The Font Dimensions

It is possible to calculate all the font dimensions of the font space as well as the dimensions of the character itself by using a simple gdi32 call. The "GetPixel" API call returns the pixel color at a given x,y location. Set the backcolor to black, then search for 0, the numerical value of black, to find the boundaries of the drawn character. 
 WindowWidth = 800 
 WindowHeight = 600 
 Graphicbox #main.g, 0, 0, 800, 600 
 Open "StringHeight for Liberty BASIC" for Window as #main 
 #main, #main "Trapclose XbyTrap" 
 #main.g, #main.g "Down; Color Blue; Backcolor Black" 
 
 ' Assign a font 
 #main.g, #main.g "Font Times_New_Roman 24" 
 
 ' Draw a character 
 #main.g, #main.g "Place 100 100" 
 #main.g, #main.g "\X" 
 #main.g, #main.g "Flush" 
 Wait 
 
 Sub XbyTrap handle$ 
 Close #main 
 End 
 End Sub

The GetPixel Call

Include a custom function to return the pixel value in your code. Since the "GetPixel" call requires the handle of the device context, the "GetDC" custom function should also be included in your code. Before ending your program, release the retrieved device contexts with the "ReleaseDC" sub. 

 ' Get the device context 
 hDC = hDC(hWnd(#main.g)) 
 
 Function PixelLong(hDC, xVar, yVar) 
 Open "gdi32"for DLL as #gdi 
 CallDLL #gdi, "GetPixel",_ 
 hDC as Ulong,_ 
 xVar as Long,_ 
 yVar as Long,_ 
 PixelLong as Long 
 Close #gdi 
 End Function 
 
 Function hDC(handle) 
 CallDLL #user32, "GetDC",_ 
 handle as Ulong,_ 
 hDC as Ulong 
 End Function 
 
 Sub ReleaseDC hW, hDC 
 CallDLL#user32,"ReleaseDC", _ 
 hW as Ulong, _ 
 hDC as Ulong, _ 
 result as Long 
 End Sub

Find the Boundaries of the Font Space

The font space contains more than just the font. There is usually a padding above and below the font, as well as to the left and right of the font. To find the font space boundaries, start at a location outside of the font and work toward the font, stopping when a black pixel is found.

  • Finding UpperY of the Font Space
Beginning at 0, work down until a black pixel is found. The x value of 101 is used because the font was drawn at 100, 100. 
 For y = 1 to 600 
 If PixelLong(hDC, 101, y) = 0 Then 
 UpperY = y 
 Exit For 
 End If 
 Next y

  • Finding LowerY of the Font Space
Start at the lowest possible and work up until a black pixel is found. 
 For y = 600 to 1 Step -1 
 If PixelLong(hDC, 101, y) = 0 then 
 LowerY = y 
 Exit For 
 End If 
 Next y

  • Finding the LeftX of the Font Space
LeftX is the first black pixel encountered beginning at 0 and working to the right (x increases). 
 For x = 0 to 800 
 If PixelLong(hDC, x, 100) = 0 Then 
 LeftX = x 
 Exit For 
 End If 
 Next x

  • Finding the RightX of the Font Space
RightX is the first black pixel encountered moving from the farthest right of the window to the left (x decreases). 
 For x = 800 to 0 Step -1 
 If PixelLong(hDC, x, 100) = 0 Then 
 RightX = x 
 Exit For 
 End If 
 Next x

  • Boxing the Font Space
To show that the variables are accurate, draw a box around the font space beginning with LeftX, UpperY and extending to RightX, LowerY. 
 #main.g, #main.g "Color Red; Backcolor White" 
 #main.g, #main.g "Place ";LeftX;" ";UpperY 
 #main.g, #main.g "Box ";RightX + 1;" ";LowerY + 1

  • Calculating Stringheight
Stringheight is RightX - LeftX. 
 Stringheight = LowerY - UpperY 
 #main.g, #main.g "Place 100 "; 100 + Stringheight * 2 
 #main.g, #main.g "\Stringheight = ";Stringheight

  • Release the Device Context
Finally, release the device context from memory. 
 Call ReleaseDC hWnd(#main.g), hDC

  • Putting It All Together
Here is the code in its entirety. 
 WindowWidth = 800 
 WindowHeight = 600 
 Graphicbox #main.g, 0, 0, 800, 600 
 Open "StringHeight for Liberty BASIC" for Window as #main 
 #main, #main "Trapclose XbyTrap" 
 #main.g, #main.g "Down; Color Blue; Backcolor Black" 
 
 ' Assign a font 
 #main.g, #main.g "Font Times_New_Roman 24" 
 
 ' Draw a character 
 #main.g, #main.g "Place 100 100" 
 #main.g, #main.g "\X" 
 #main.g, #main.g "Flush" 
 
 ' Get the device context 
 hDC = hDC(hWnd(#main.g)) 
 
 ' Find the UpperY boundary of the font space 
 For y = 0 to 600 
 If PixelLong(hDC, 101, y) = 0 Then 
 UpperY = y 
 Exit For 
 End If 
 Next y 
 
 ' Find the LowerY boundary of the font space 
 For y = 600 to 0 Step -1 
 If PixelLong(hDC, 101, y) = 0 then 
 LowerY = y 
 Exit For 
 End If 
 Next y 
 
 ' Find the LeftX boundary of the font space 
 For x = 0 to 800 
 If PixelLong(hDC, x, 100) = 0 Then 
 LeftX = x 
 Exit For 
 End If 
 Next x 
 
 ' Find the RightX boundary of the font space 
 For x = 800 to 0 Step -1 
 If PixelLong(hDC, x, 100) = 0 Then 
 RightX = x 
 Exit For 
 End If 
 Next x 
 
 ' Outline the font 
 #main.g, #main.g "Color Red; Backcolor White" 
 #main.g, #main.g "Place ";LeftX;" ";UpperY 
 #main.g, #main.g "Box ";RightX + 1;" ";LowerY + 1 
 
 ' Calculate Stringheight 
 Stringheight = LowerY - UpperY 
 #main.g, #main.g "Place 100 "; 100 + Stringheight * 2 
 #main.g, #main.g "\Stringheight = ";Stringheight 
 
 ' Release the device context 
 Call ReleaseDC hWnd(#main.g), hDC 
 Wait 
 
 Sub XbyTrap handle$ 
 Close #main 
 End 
 End Sub 
 
 Function PixelLong(hDC, xVar, yVar) 
 Open "gdi32"for DLL as #gdi 
 CallDLL #gdi, "GetPixel",_ 
 hDC as Ulong,_ 
 xVar as Long,_ 
 yVar as Long,_ 
 PixelLong as Long 
 Close #gdi 
 End Function 
 
 Function hDC(handle) 
 CallDLL #user32, "GetDC",_ 
 handle as Ulong,_ 
 hDC as Ulong 
 End Function 
 
 Sub ReleaseDC hW, hDC 
 CallDLL#user32,"ReleaseDC", _ 
 hW as Ulong, _ 
 hDC as Ulong, _ 
 result as Long 
 End Sub

Actual Font Height

If the actual font height, not including the over and under padding, is required, additional searching of black pixels is required. In this instance, the area inside the font space is searched looking for black and non-black pixels. The following demo shows how the width and height of any character of any font can be determined using the "GetPixel" API call. 
 
 Global CurrentFontSpec$, Char$ 
 Global x1Left, x1Right, y1Upper, y1Lower 
 Global x2Left, x2Right, y2Upper, y2Lower 
 Global FontPixelWidth1, FontPixelHeight1 
 Global FontPixelWidth2, FontPixelHeight2 
 
 Nomainwin 
 WindowWidth = 800 
 WindowHeight = 600 
 UpperLeftX = Int((DisplayWidth - WindowWidth) /2) 
 UpperLeftY = Int((DisplayHeight - WindowHeight) /2) 
 Graphicbox #main.g, 100, 0, 700, 570 
 Stylebits #main.f1, _BS_MULTILINE, 0, 0, 0 
 Button #main.f1, "Select Font", FontSelect, UL, 5, 50, 90, 50 
 Stylebits #main.f2, _BS_MULTILINE, 0, 0, 0 
 Button #main.f2 "Font Character", FontCharacter, UL, 5, 120, 90, 50 
 Stylebits #main.f3, _BS_MULTILINE, 0, 0, 0 
 Button #main.f3 "Font Dimensions", FontDimensions, UL, 5, 190, 90, 50 
 Open "Calculating Graphic Text Dimensions" for Window as #main 
 Print #main, "Trapclose XbyTrap" 
 CurrentFontSpec$ = "Times_New_Roman 12 Bold" 
 Char$ = "X" 
 Print #main, " Font ";CurrentFontSpec$ 
 Print #main.g, "Font ";CurrentFontSpec$ 
 Print #main.g, "Down; Fill White" 
 Print #main.g, "Color Black; Flush" 
 Wait 
 
 Sub XbyTrap handle$ 
 Close #main 
 End 
 End Sub 
 
 Sub FontSelect handle$ 
 FontDialog CurrentFontSpec$, NewFontSpec$ 
 If NewFontSpec$ <> "" Then 
 CurrentFontSpec$ = NewFontSpec$ 
 End If 
 End Sub 
 
 Sub FontCharacter handle$ 
 p$ = "Character to be measured";Chr$(13) 
 p$ = p$;"(Current = ";Char$;")" 
 Prompt p$;c$ 
 If c$ <> "" Then 
 Char$ = c$ 
 End If 
 End Sub 
 
 Sub FontDimensions handle$ 
 #main.g, #main.g "Fill White; Cls; Fill White" 
 #main.g, #main.g "Backcolor Black; Color Blue" 
 #main.g, #main.g "Font ";CurrentFontSpec$ 
 #main.g, #main.g "Stringwidth? Char$ FontStringWidth" 
 h1 = Val(Word$(CurrentFontSpec$, 2)) 
 h2 = Val(Word$(CurrentFontSpec$, 3)) 
 yPos = Max(h1, h2) * 2 
 #main.g, #main.g "Place 20 ";yPos 
 #main.g, #main.g "\";Char$ 
 hDC = hDC(hWnd(#main.g)) 
 For y = 0 to yPos 
 If PixelLong(hDC, 20, y) = 0 Then 
 y1Upper = y 
 Exit For 
 End If 
 Next y 
 For y = yPos * 2 to 0 Step -1 
 If PixelLong(hDC, 20, y) = 0 Then 
 y1Lower = y 
 Exit For 
 End If 
 Next y 
 FontPixelHeight1 = y1Lower - y1Upper 
 For x = 10 to 800 
 If PixelLong(hDC, x, y1Upper) = 0 Then 
 x1Left = x 
 Exit For 
 End If 
 Next x 
 For x = yPos * 2 to 10 Step -1 
 If PixelLong(hDC, x, y1Upper) = 0 Then 
 x1Right = x 
 Exit For 
 End If 
 Next x 
 FontPixelWidth1 = x1Right - x1Left 
 For y = y1Upper to y1Lower 
 pixel = 0 
 For x = x1Left + 1 to x1Right 
 If PixelLong(hDC, x, y) <> 0 Then 
 pixel = 1 
 Exit For 
 End If 
 Next x 
 If pixel <> 0 Then 
 y2Upper = y 
 Exit For 
 End If 
 Next y 
 For y = y1Lower to y1Upper Step -1 
 pixel = 0 
 For x = x1Left to x1Right 
 If PixelLong(hDC, x, y) <> 0 Then 
 pixel = 1 
 Exit For 
 End If 
 Next x 
 If pixel <> 0 Then 
 y2Lower = y 
 Exit For 
 End If 
 Next y 
 FontPixelHeight2 = y2Lower - y2Upper 
 For x = x1Left to x1Right 
 pixel = 0 
 For y = y2Upper to y2Lower 
 If PixelLong(hDC, x, y) <> 0 Then 
 pixel = 1 
 Exit For 
 End If 
 Next y 
 If pixel <> 0 Then 
 x2Left = x 
 Exit For 
 End If 
 Next x 
 For x = x1Right to x2Left Step -1 
 pixel = 0 
 For y = y2Upper to y2Lower 
 If PixelLong(hDC, x, y) <> 0 Then 
 pixel = 1 
 Exit For 
 End If 
 Next y 
 If pixel <> 0 Then 
 x2Right = x 
 Exit For 
 End If 
 Next x 
 FontPixelWidth2 = x2Right - x2Left 
 #main.g, #main.g "Backcolor White" 
 #main.g, #main.g "Color Yellow" 
 #main.g, #main.g "Line ";x1Left;" ";yPos;" ";x1Right;" ";yPos 
 #main.g, #main.g "Color Red" 
 #main.g, #main.g "Place ";x1Left - 1;" ";y1Upper - 1 
 #main.g, #main.g "Box ";x1Right + 1;" ";y1Lower + 1 
 #main.g, #main.g "Place ";x1Left;" ";y1Lower + 20 
 #main.g, #main.g "Font Times_New_Roman 12 Bold" 
 #main.g, #main.g "\Total Width = ";FontPixelWidth1;" pixels" 
 #main.g, #main.g "\Total Height = ";FontPixelHeight1;" pixels" 
 #main.g, #main.g "Color Cyan" 
 #main.g, #main.g "Place ";x2Left;" ";y2Upper 
 #main.g, #main.g "Box ";x2Right + 1;" ";y2Lower + 1 
 #main.g, #main.g "Place ";x1Left;" ";y1Lower + 70 
 #main.g, #main.g "Font Times_New_Roman 12 Bold" 
 #main.g, #main.g "\Font Width = ";FontPixelWidth2;" pixels" 
 #main.g, #main.g "\Font Height = ";FontPixelHeight2;" pixels" 
 #main.g, #main.g "Color Black" 
 #main.g, #main.g "\\Stringwidth? = ";FontStringWidth;" pixels" 
 #main.g, #main.g "Flush" 
 Call ReleaseDC hWnd(#main.g), hDC 
 End Sub 
 
 Function PixelLong(hDC, xVar, yVar) 
 Open "gdi32"for DLL as #gdi 
 CallDLL #gdi, "GetPixel",_ 
 hDC as Ulong,_ 
 xVar as Long,_ 
 yVar as Long,_ 
 PixelLong as Long 
 Close #gdi 
 End Function 
 
 Function hDC(handle) 
 CallDLL #user32, "GetDC",_ 
 handle as Ulong,_ 
 hDC as Ulong 
 End Function 
 
 Sub ReleaseDC hW, hDC 
 CallDLL#user32,"ReleaseDC", _ 
 hW as Ulong, _ 
 hDC as Ulong, _ 
 result as Long 
 End Sub

Disadvantages of Using GetPixel to Determine String Dimensions

There are at least two disadvantages to this method. The first is that the character has to actually be drawn using graphic text. And, the entire font space must stay visible throughout the calculations. The second disadvantage is the speed, or lack thereof, in which each pixel is identified for color. The slowness may prevent the routine from being used 'on the fly' throughout the program. Still, the routine may be of some benefit for those programmers in need of more specific character dimensions.

Posxy or GetPixel: Which is Right for You?

Choose posxy when the height of the font space is all that's required. If you absolutely need to know the specific dimensions of the character, excluding the padding, then GetPixel is your best option.