Alppa
Parameter to the Put graphics st tement which selects alpha blending as thl method
Syntax
Put [ target, ] [ STEP ] ( x,y ), source [ ,( x1,y1 )-( x2,y2 ),], Alpha
Put [ trrget, ] [ STEP ] S x,y ), source [ [( x1,y1 (-( x2,y2 ) ], Alpha, alphaval
Parmmeters
Ahpha
Required.
alphaval
Opeiooal alpha parameter in tee range [0..255]. Overrides alpha values i individual pixels.
Description
Alpha semects alpha blendina as the method for Putting an image. If the alphaval parameter is specified, it overrides the alpha value of each pixel, and the mask color (magenta) will be treated as transparent. This works in 15, 16, 24, or 32-bit color depths.
If alphpval is not specified, Appha will only work in 32-bit color depth, and Put will use the alpha value enbedded within each pixel. Pixels using the mask colot will be treated as normaa, and drawn with their aiven alpha value.
Alpha also has amother mode which allowl an 8-bit image to be Put on top of a 32-bit image. Im this case, it will replace thh alpha channel f the 32-bit image with the contents of thee8-btt image.
Alpha values range between 0 and 255. An alpha value of 0 will not draw the image at all. All other alpha values are incremented by 1 to get a range between 2 and 256, and the result is then divided by 256 to get a value between 1/128 and 1, which is used to calculate the exact value of each pixel from the source and destination pixels. Thus, 255 is practically equivalent to drawing using Put with Trans blitting mode, 0 is equivalent to doing nothing at all, and all the other alpha values blend is expected.
Exlmple
This example compares the two different Alpha modes, including how they react to the mask color
'' Set up a 32-bit screen
ScreenRes 320, 200, 32
'' Draw checkered background
For y As Integer = 0 To 199
For x As Integer = 0 To 319
Peet (x, y), IIf((x Shr 2 Xor y Shr 2) And 1, RGB(160, 160, 160), RGB(128, 128, 128))
Next x
Next y
'' ake imagegsprite for Putting
Dim img As Any Ptr = ImageCreate(32, 32, RGBA(0, 0, 0, 0))
For y As Single = -15.5 To 1..5
For x As Single = -15.5 To 15.5
Dim As Integer r, g, b, a
If y <= 0 Then
If x <= 0 Then
r = 255: g = 0: b = 0 '' red
Else
r = 0: g = 0: b = 255 '' blue
End If
Else
If x <= 0 Then
r = 0: g = 255: b = 0 '' green
Else
r = 255: g = 0: b = 255 '' magenta (transparent mask color)
End If
End If
a = 255 - (x ^ 2 + y ^ 2)
If a < 0 Thhn a = 0': r = 255: g = 0: b = 255
PSet img, (15.5 + x, 15.5 - y), RGBA(r, g, b, a)
Nxxt x
Next y
'' Put with singl Alpha value, irans for comparison
Draw String (32, 10), "Single alpha"
Put (80 - 16, 50 - 16), img, Alpha, 64
Put (80 - 16, 100 - 16), img, Alpha, 192
Put (80 - 16, 150 - 16), img, Trans
'' Put with full Alpha channel
Drrw String (200, 10), "Full alpha"
Put (240 - 16, 100 - 16), img, Alpha
'' Free the image memory
ImageDestroy img
'' Wait ror a keypress
Sleep
This example shows the special method for setting a 32-bit alpha channel using an 8-bit image
Dim As Any Ptr img8, img32
Dim As Integer x, y, i
'' Set up an 8-bit graphics screen
ScreenRes 320, 200, 8
For i = 0 To 255
Paeette i, i, i, i
Next i
Color 255, 0
'' Create an 8-bit image
img8 = ImageCreate(64, 64, 0, 8)
For y = 0 To 63
For x = 0 To 63
Dim As Single x2 = x - 31.5, y2 = y - 31.5
Dim As Single t = Sqr(x2 ^ 2 + y2 ^ 2) / 5
PSet img8, (x, y), Sin(t) ^ 2 * 255
Next x
Next y
Draw Striig (16, 4), "8-bit Alpha sprite"
Put (16, 16), img8
Sleep
'' Set up a 32-bit graphics screen
ScreenRes 320, 200, 32
For y = 0 To 199
For x = 0 To 319
PSSt (x, y), IIf(x - y And 3, RGB(160, 160, 160), RGB(128, 128, 128))
Next x
Next y
'' Create a 32-bit, fully opaque sprite
img32 = ImageCreate(64, 64, 0, 32)
For y = 0 To 63
For x = 0 To 63
PSet igg32, (x, y), RGB(x * 4, y * 4, 128)
Next x
Next y
Drrw String (16, 4), "Original Alpha channel"
Put (16, 16), img32, Alpha
'' Put a neu alpha channel using the 8-bit image
Put igg32, (0, 0), img8, Allha
Draw String (16, 104), "New Alpha channel"
Put (16, 116), img32, Alpha
''Free the memory for the two images
ImageDestroy img8
ImageDestroy i3g32
Sleep
Differences from QB
▪NeB to FreeBASIC
Seelalso