How to draw a triangle?

You can't draw a filled triangle (or a circle, or a polygon, or...) with the 2D API. If you want to hack it, you could potentially draw a rectangle, rotate it to the desired angle, clip it and then rotate it back. Or, you could carve it out of a rectangle with a fully transparent rectangle rotated to the desired angles and drawn on top with alpha blending disabled.

Endless beat me to it but it seems the only way is to hack it with squares and rectangles. Pretty glaring omission from a 2D API. IMO.

Library "v30/bslDefender.brs"
Sub Main()
	font_registry = CreateObject("roFontRegistry")
	font = font_registry.GetDefaultFont()
	codes = bslUniversalControlEventCodes()
    m.screen=CreateObject("roScreen", true)
    m.msgport=CreateObject("roMessagePort")
    m.screen.SetPort(m.msgport)
    m.screen.Clear(&h394837FF)
    m.screen.SetAlphaEnable(true)
    m.screen.DrawText("background", 530, 250, &hebebebFF, font)
    
    square = CreateObject("roBitmap", {width: 400, height: 400, AlphaEnable: true})
  	square.Clear(&h25344399)
  	rect = CreateObject("roBitmap", {width: 565, height: 280, AlphaEnable: false})
  	rect.drawRotatedobject( 0, 285, 45, square)
  	m.screen.drawobject(357, 220, rect)
    m.screen.Swapbuffers()
   	rowrow = 0	
   	
   	while true
   	m.screen.Clear(&h394837FF)
   	m.screen.DrawText("background", 530, 250, &hebebebFF, font)
   	msg = m.msgport.getmessage()
    if type(msg) = "roUniversalControlEvent"
   	button = msg.getint()
   	if button=codes.BUTTON_RIGHT_PRESSED	
   	rowrow = rowrow + 45
   	m.screen.drawRotatedobject(357, 220, rowrow, rect)
   	m.screen.Swapbuffers()
   	end if
  	end if
   	end while
End Sub

"TheEndless" wrote:
If you want to hack it, you could potentially draw a rectangle, rotate it to the desired angle, clip it and then rotate it back. Or, you could carve it out of a rectangle with a fully transparent rectangle rotated to the desired angles and drawn on top with alpha blending disabled.

That surely is an evil hack but i am interested in trying it. I understand it conceptually but for now the 2D mechanics (esp. roRegions) are way over my head. Can you sketch the two approaches - as sequence of steps/components used to form triangle in a new bitmap? Broad strokes, no need code to work or make actual triangle - i can RTFM and try for the rest.

Actually, nevermind. It seems that DrawRotatedObject() only supports arbitrary angles on devices with OpenGL support. I guess that's why they never updated the documentation.

The only other way I can think to do it would be something like this, but it's likely to produce jaggies. It does run faster than I expected, though...

' This will create a right triangle lying on its long side
' Create a bitmap the size of the outer bounds of the triangle
' Make sure alpha enable is false, so the lines cut through the bitmap
triangle = CreateObject("roBitmap", { Width: 400, Height: 200, AlphaEnable: False })
' Clear the bitmap to the color you want
triangle.Clear(&HFFFFFFFF)
' Clear out the left slope
For x = 0 To 200
    triangle.DrawLine(x, 0, x - 200, 200, &H00000000)
Next
' Clear out the right slope
For x = 200 To 400
    triangle.DrawLine(x, 0, x + 200, 200, &H00000000)
Next

"TheEndless" wrote:
It seems that DrawRotatedObject() only supports arbitrary angles on devices with OpenGL support. I guess that's why they never updated the documentation.

What! :shock:
You mean the 27x0 line (RokuLT/Roku1/Roku2) - the joy and pride of RokuCo from Sep 2013 - cannot rotate to angles <> 90*n ?
What about Roku3, can it?

This shatters my belief, which was based on viewtopic.php?f=34&t=56314&p=432102#p432100
The suspicious silence of Roku* on the question suddenly seems to speak volumes. :oops:

"EnTerr" wrote:

"TheEndless" wrote:
It seems that DrawRotatedObject() only supports arbitrary angles on devices with OpenGL support. I guess that's why they never updated the documentation.

What! :shock:
You mean the 27x0 line (RokuLT/Roku1/Roku2) - the joy and pride of RokuCo from Sep 2013 - cannot rotate to angles <> 90*n ?
What about Roku3, can it?

This shatters my belief, which was based on viewtopic.php?f=34&t=56314&p=432102#p432100
The suspicious silence of Roku* on the question suddenly seems to speak volumes. :oops:

I'm guessing at the "OpenGL" support being required, but if it is, then it should work on Roku 3. I have my dev Roku 3 disconnected at the moment, to avoid the temptation to use it while I work on a 2D API channel, so I can't test it right now...

Here is a quick ROKU 3 example, since I don't have your will power. I unplugged my 2XD

 
   Screen = CreateObject( "roScreen", True )
   Screen.Clear( &hFFFFFFFF )
   Screen.SwapBuffers()
   
   bitmap = CreateObject( "roBitmap", { width: 200, height: 200 , AlphaEnable: False } )
   bitmap.Clear( &h911820FF )
   width  = bitmap.GetWidth()
   height = bitmap.GetHeight()
   region = CreateObject( "roRegion", bitmap, 0, 0, width, height )
   
   x = int( width  / 2 )
   y = int( height / 2 )
   region.SetPretranslation( -x, -y )
   
   for theta = 360 to 0 step -1
      Screen.Clear( &hFFFFFFFF )
      Screen.DrawRotatedObject( 100 + x, 100 + y, theta, region )
      Screen.SwapBuffers()  
   end for

If an "Ode to the triangle" were needed, this video would do:
https://www.youtube.com/watch?v=KdyvizaygyY

I know this thread is a bit old, but since triangles are so common I thought I'd relay what I think is an important point...

You CAN draw solid-color triangles with any arbitrary 3 points as corners. You won't be able to draw them quickly though, and you'll need to do a lot of computation in B.Script.
Google/Bing/Search for "triangle rasterizer" and also maybe "Graphics Gems". There's even logic for triangle rasterization published in that Graphics Gems book (Maybe vol III...I don't remember) if you can find it.

Basically, you decide which side (left/top or right/bottom) will get it's end-points included, and then draw horizontal lines at the proper starting points and ending points moving from top to bottom. Think TV scan lines as the horizontal lines you're drawing where they "fit" the triangle.

This type of stuff was common in "the old days" before GPUs.

This can be extended to other shapes also...polygons and even circles. Convex shapes or concave shapes where no horizontal line crosses multiple start/end points. You basically do the computations for the edges of the "scan line overlap" (AKA rasterize the shape) and pass an array of points to a rasterizer-drawing routine that draws the horizontal lines in a given color.

It's slow in B.Script though. I wrote a simple one a year or two ago, but it wasn't fast enough for my needs so I abandoned it. Maybe you'll do better. Once you have the shape, you can always put it in a texture and blit it quickly...until you need to "reshape" it. Then you re-compute.

"MazeWizzard" wrote:
I know this thread is a bit old, but since triangles are so common I thought I'd relay what I think is an important point...
...
It's slow in B.Script though. I wrote a simple one a year or two ago, but it wasn't fast enough for my needs so I abandoned it. Maybe you'll do better. Once you have the shape, you can always put it in a texture and blit it quickly...until you need to "reshape" it. Then you re-compute.

Thank you for chiming in. Thread is not too old, i have neither solved, nor given up on the idea i have (just haven't got developing on it - i have small list of things i work on, on and off).

I did think of scan-line rasterizing (it's not hard but will have to be careful with degenerate cases, like all 3 vertices on same horizontal line + alpha blending). Initially i was concerned that when i am working in non-native resolution (say if i use roScreen is 854x480 when player is in 720p or 1080p mode), that will lead to triangles turning into horizontal stripes, with gaps forming between the horizontal lines i draw due to zooming. I did not find discussion anywhere how the scaling is done - it could be vector or bitmap-wise, with different outcomes. I still don't know for sure and since it is not documented, it can potentially change (?!).

But performance is my biggest concern - as an idea of speed i would hope to be able to draw something like this spinning tetrahedron:

My gut feeling is line-by-line won't be able to. Was your routine close to such speed, ballpark?