Canvases and Alpha

BlitzMax Forums/MaxGUI Module/Canvases and Alpha

Adam Novagen

(Posted 2016) [#1]

So I'm cobbling together a small tool to aid me in the creation of a larger project, but finding myself repeatedly bogged down with a lack of understanding (or decent documentation) of MaxGUI. My current issue is drawing on a canvas with alpha enabled. Have a microversion of my current issue:

SuperStrict

' Bonus question: why is this Import necessary if BlitzMax builds your code with ALL modules by default?
Import maxgui.Drivers

Global mainWindow:tGadget = CreateWindow("Canvas example",0,0,800,600,Null,WINDOW_DEFAULT + WINDOW_CENTER)

Global canvas:tGadget = CreateCanvas(0,0,ClientWidth(mainWindow),ClientHeight(mainWindow),mainWindow)
	SetGadgetLayout canvas,EDGE_ALIGNED,EDGE_ALIGNED,EDGE_ALIGNED,EDGE_ALIGNED
Global canvasTimer:tTimer = CreateTimer(60) ' Refresh canvas at 60 fps
Global cursorX:Int,cursorY:Int

Global quit:Int

While Not quit
	WaitEvent()
	
	Select EventID()
		Case EVENT_MOUSEMOVE
			cursorX = EventX()
			cursorY = EventY()
		Case EVENT_WINDOWCLOSE
			If EventSource() = mainWindow Then quit = True
		Case EVENT_TIMERTICK
			If EventSource() = canvasTimer Then updateCanvas()
	EndSelect
Wend

End

Function updateCanvas()
	SetGraphics CanvasGraphics(canvas)
	
	SetClsColor 0,0,191
	Cls
	
	SetColor 0,0,0
	SetAlpha 1
	DrawRect cursorX - 32,cursorY - 32,64,64
	SetColor 255,0,255
	DrawRect cursorX - 32,cursorY - 32,32,32
	DrawRect cursorX,cursorY,32,32
	
	SetColor 255,255,255
	SetAlpha .6
	DrawOval cursorX - 16,cursorY - 16,32,32
	
	Flip
EndFunction

As you can see, the circle is supposed to be drawn at 60% alpha, but has no transparency applied to it. If the alpha is set to .5 or below, the circle disappears completely. So, is there a way to support a proper alpha buffer on a canvas?

Adam Novagen

(Posted 2016) [#2]

WOW never mind, I had completely forgotten that it's necessary to call SetBlend ALPHABLEND to enable alpha blending. Dear god, I've clearly been banging my head against the wall too much today, I should give it a rest for tomorrow.

Bonus question from the code sample still stands though: why is Import MaxGUI.Drivers necessary to use MaxGUI? I thought BlitzMax just pulled in every single module at build unless you used the Framework command, but then I still only have a somewhat dim understanding of modules, imports and frameworks.

RustyKristi

(Posted 2016) [#3]

Try using the framework assistant, just do a site search and you'll find it :)

Adam Novagen

(Posted 2016) [#4]

I have the framework assistant, I use it for finalizing a build so I can shrink the executable. My question is why an Import command would be necessary at all if Framework isn't being used. Anyway, the main topic for this thread is resolved so I'd do better to address that question to a different subforum.