OpenGL Screen Grab

General
1

I’m trying to get the contents of an OpenGL rendering into a Picture.
DrawInto doesn’t seem to work.
I’ve been looking for standard function within OpenGL, but it doesn’t seem to exist.

Anyone know how to do this within Xojo?

2

Sorry folks, I think I can answer my own question…

Is that the right handling of the alpha channel?

[code]Public Function getPicture() as Picture

dim m as MemoryBlock = new MemoryBlock( widthheight4)

openGL.glReadPixels 0,0,me.Width, me.Height, openGL.GL_RGBA, openGL.GL_UNSIGNED_BYTE, m

dim p as new picture(me.Width, me.Height)
dim pm as new Picture(me.Width, me.Height)

dim i as integer = 0
dim h, w as integer
dim a as integer

for h = me.Height downTo 1
for w = 1 to me.Width
p.RGBSurface.Pixel(w,h) = rgb(m.Byte(i), m.Byte(i+1), m.Byte(i+2))
a = 255-m.Byte(i+3)
pm.RGBSurface.pixel(w,h) = rgb(a,a,a)
i=i+4
next
next

p.ApplyMask pm

return p

End Function[/code]

3

Some years ago I found this code in the forum. I use it to create a PNG files not from the screen but from the OpnGLSurface control.
It has worked without problems so far.

[code]Function getPicture(glSurf As OpenGLSurface) As Picture

'Capture OpenGLSurface image and puts it into a PNG file

//calculate sizes
dim w As integer = glSurf.Width
dim h As integer = glSurf.Height
dim pad As integer = w mod 4
dim totalBytes As integer = (w * h * 3) + (h * pad)

//create and fill memoryblock with pixel data
glSurf.MakeCurrent
dim m As MemoryBlock = New MemoryBlock(totalBytes)
OpenGL.glReadPixels(0, 0, w, h, OpenGL.GL_BGR, OpenGL.GL_UNSIGNED_BYTE, m)

//create output picture
dim p As Picture = New Picture(w, h, 32)
dim surf As RGBSurface = p.RGBSurface

//scan memoryblock into picture
h = h - 1
w = w - 1
dim x, y, offset As integer //offset starts at 0
for y = h downto 0
for x = 0 to w
surf.Pixel(x, y) = m.ColorValue(offset, 24)
offset = offset + 3
next
offset = offset + pad //skip per line
next

return p //store picture

Exception
LOG "Error: " + CurrentMethodName

End Function[/code]