image alpha layer + text

Nico · Post by **Nico** » Fri Jun 22, 2007 8:06 pm

Hello,

I would need your assistance to work on images with a alpha layer.

Here my problem:
I charge an image with a layer alpha and it is impossible for me to add on this image of the text, the text which I writes above becomes transparent! Twisted Evil

Of course one can draw the image on the support and then to draw the text and there not problem but I need absolutely to add text on the image directly.

Have already work yourself above?

netmaestro · Post by **netmaestro** » Sat Jun 23, 2007 4:06 am

I'm not 100% sure I get what you mean, but I think you want to draw semi-transparent text onto an image. If that's the ticket, there are several ways to do it. Here's one of the simplest, a homebrewed solution using nearly all PB native functions, just a touch of API:

Code: Select all

; Some mischief for a Friday evening... 
; by netmaestro 


Procedure ConvertToAlpha(image, transcolor, intensity) 

  Structure BGRA 
    blue.c 
    green.c 
    red.c 
    alpha.c 
  EndStructure 

  GetObject_(ImageID(image), SizeOf(BITMAP), bmp.BITMAP) 
  *bits.BGRA = bmp\bmBits 
  For i=0 To bmp\bmHeight-1 
    For j=0 To bmp\bmWidthBytes-1 Step 4 
      *px.BGRA = *bits + bmp\bmWidthBytes * i + j 
      If *px\blue=Blue(transcolor) And *px\green=Green(transcolor) And *px\red=Red(transcolor) 
        *px\alpha = 0 
      Else 
        *px\alpha = intensity 
      EndIf 
    Next 
  Next 
  
EndProcedure 


;================================================================================ 
; Step 1 

; Create a 32-bit image to use for your text 
; Make the background color close to the text color, just noticeably darker 
; Draw your text on the background 
;================================================================================ 


LoadFont(0, "Arial", 48, #PB_Font_Bold|#PB_Font_HighQuality) 
CreateImage(0, 400, 70, 32) 
StartDrawing(ImageOutput(0)) 
  Box(0,0,400,70,RGB(230,0,0)) 
  DrawingFont(FontID(0)) 
  DrawText(0,0, "Alpha Text", #Red, RGB(230,0,0)) 
StopDrawing() 


;================================================================================ 
; Step 2 

; Apply an alpha value to all non-transparent pixels in your text image 
; using the supplied ConvertToAlpha procedure 
;================================================================================ 


ConvertToAlpha(0, RGB(230,0,0), 90) 


;================================================================================ 
; Step 3 

; Create or load an image of any desired depth to draw the text on 
; here we'll just create one 
;================================================================================ 


CreateImage(1, 600,400) 
StartDrawing(ImageOutput(1)) 
  Box(0,0,200,200,#White) 
  Box(200,0,200,200,#Gray) 
  Box(400,0,200,200,#White) 
  Box(0,200,200,200,#Gray) 
  Box(200,200,200,200,#White) 
  Box(400,200,200,200,#Gray) 
StopDrawing() 


;================================================================================ 
; Step 4 

; Use PureBasic's DrawAlphaImage command to imprint the text on the image 
;================================================================================ 


StartDrawing(ImageOutput(1)) 
  DrawAlphaImage(ImageID(0), 110, 160) 
StopDrawing() 


;================================================================================ 
; You're finished! Give it a test:  
;================================================================================ 


OpenWindow(0,0,0,600,400,"",$CA0001) 
CreateGadgetList(WindowID(0)) 
ImageGadget(0,0,0,0,0,ImageID(1)) 
Repeat:Until WaitWindowEvent()=#WM_CLOSE

Nico · Post by **Nico** » Sat Jun 23, 2007 10:58 am

Thank's for the code but my problem is :

I have a png image with alpha, I wants to add text on this image but the text become transparent!!

Code: Select all

UsePNGImageDecoder()

Global OriginProc.l

LoadFont (1, "Arial", 30) 

LoadImage(0,"c:\image.png")

hdc =StartDrawing(ImageOutput(0))
If hdc
  SetBkMode_(hdc,#TRANSPARENT)
  SetTextColor_(hdc,RGB(255,255,0))
  texte.s="Nico"
  DrawingFont(FontID(1))
  DrawText(10,20,"texte")
  StopDrawing()
EndIf 

Procedure WindowCallback(Window, message, wParam, lParam) 
  Select message
    Case #WM_PAINT
      Debug "#WM_PAINT"
      
      ps.PAINTSTRUCT
      BeginPaint_(Window,ps)
      EndPaint_(Window,ps)
      
      hdc =StartDrawing(WindowOutput(0))
      If hdc
        DrawAlphaImage(ImageID(0),0,0)
        StopDrawing()
      EndIf 
      ProcedureReturn 0
      
  EndSelect 
  ProcedureReturn CallWindowProc_(OriginProc,Window, message, wParam, lParam) 
EndProcedure


If OpenWindow(0, 100, 200, 400, 400, "PureBasic Window", #PB_Window_SystemMenu | #PB_Window_MinimizeGadget | #PB_Window_MaximizeGadget)
  
  OriginProc=SetWindowLong_(WindowID(0),#GWL_WNDPROC,@WindowCallback())
  
  CreateGadgetList(WindowID(0))
  
  Repeat
    EventID = WaitWindowEvent()
    
    If EventID = #PB_Event_CloseWindow  ; If the user has pressed on the close button
      Quit = 1
    EndIf
    
  Until Quit = 1
  
EndIf

netmaestro · Post by **netmaestro** » Sat Jun 23, 2007 6:10 pm

Please post your image, I'd like to explore it further but I want to be sure of what's going on.

Nico · Post by **Nico** » Sat Jun 23, 2007 7:54 pm

netmaestro · Post by **netmaestro** » Sat Jun 23, 2007 9:08 pm

Ok, good. The problem is that the alpha values in the text portion are zeroed out, causing the text pixels to be ignored by the DrawAlphaImage. The code I already gave you can be used to solve it, just added to what you already have:

Code: Select all

Procedure ConvertToAlpha(image, transcolor, intensity)

  Structure BGRA
    blue.c
    green.c
    red.c
    alpha.c
  EndStructure

  GetObject_(ImageID(image), SizeOf(BITMAP), bmp.BITMAP)
  *bits.BGRA = bmp\bmBits
  For i=0 To bmp\bmHeight-1
    For j=0 To bmp\bmWidthBytes-1 Step 4
      *px.BGRA = *bits + bmp\bmWidthBytes * i + j
      If *px\blue=Blue(transcolor) And *px\green=Green(transcolor) And *px\red=Red(transcolor)
        *px\alpha = 0
      Else
        *px\alpha = intensity
      EndIf
    Next
  Next
  
EndProcedure


UsePNGImageDecoder() 

Global OriginProc.l 

LoadFont (1, "Arial", 30) 

LoadImage(0,"image.png") 

CreateImage(1, 85,40,32)
StartDrawing(ImageOutput(1))
  DrawingFont(FontID(1))
  Box(0,0,85,40,RGB(220,220,0))
  DrawText(0,0,"texte",RGB(255,255,0),RGB(220,220,0))
StopDrawing()

ConvertToAlpha(1, RGB(220,220,0),255)

StartDrawing(ImageOutput(0)) 
  DrawAlphaImage(ImageID(1),10,24)
StopDrawing() 

Procedure WindowCallback(Window, message, wParam, lParam) 
  Select message 
    Case #WM_PAINT 
 
      ps.PAINTSTRUCT 
      BeginPaint_(Window,ps) 
      EndPaint_(Window,ps) 
      
      hdc =StartDrawing(WindowOutput(0)) 
      If hdc 
        DrawAlphaImage(ImageID(0),0,0) 
        StopDrawing() 
      EndIf 
      ProcedureReturn 0 
      
  EndSelect 
  ProcedureReturn CallWindowProc_(OriginProc,Window, message, wParam, lParam) 
EndProcedure 


If OpenWindow(0, 100, 200, 400, 400, "PureBasic Window", #PB_Window_SystemMenu | #PB_Window_MinimizeGadget | #PB_Window_MaximizeGadget) 
  
  OriginProc=SetWindowLong_(WindowID(0),#GWL_WNDPROC,@WindowCallback()) 
  
  CreateGadgetList(WindowID(0)) 
  
  Repeat 
    EventID = WaitWindowEvent() 
    
    If EventID = #PB_Event_CloseWindow  ; If the user has pressed on the close button 
      Quit = 1 
    EndIf 
    
  Until Quit = 1 
  
EndIf

Seems to give the desired result.

Nico · Post by **Nico** » Sat Jun 23, 2007 9:29 pm

thank you