Latest revision as of 06:52, 13 October 2018

Shrinking (also known as scaling, reduction, and "zooming") is a hardware feature of the NeoGeo which allows to scale down sprites with per-pixel accuracy in both dimensions.

Shrinking is performed by LSPC by skipping a variable number of pixel lines or columns. It can be seen as a simple subsampling of the original graphics since there's no smoothing applied at all.

Vertical shrinking

The vertical shrinking is set by an 8-bit value specifying the final height of the sprite's graphics. This value is set in VRAM, in the SCB2.

Range: $FF is the tallest, $0 is the smallest.

To know which line to skip, LSPC uses a lookup table stored in the L0 ROM.

The vertical shrink parameter propagates in chained sprites.

Caveat: Display window

Note that vertical shrinking does not affect the tile height setting of the sprite. The graphics are shrunk inside the defined window.

Sprite height set to 4 tiles, graphics intentionally filling 4 tiles
The same sprite updated to be only 3 tiles high without clearing the 4th (yellow) tile
The sprite will shrink this way, showing the garbage yellow tile from the previous setup

Caveat: Last line repeat

If the display window of a sprite is taller than the shrunk graphics, the remaining lines will be filled with repeats of the last line of the last tile (the bottom line of the tile at map index 15).

SNK recommends leaving that line fully transparent if this causes problems.

Horizontal shrinking

The horizontal shrinking is set by a 4-bit value specifying the final width of the sprite graphics +1 (giving 1 to 16 pixels wide sprites). This value is also set in SCB2.

Range: $F is full size (all 16 pixels shown), $0 is the smallest (only 1 pixel shown).

The horizontal shrink parameter does not propagate in chained sprites. Values for each sprite of a group have to be distributed to obtain the total desired group width.

There is no external lookup table for horizontal shrinking. The process is completely done inside LSPC. In the following table, each line corresponds to a shrinking value. 1 means the pixel will be drawn and 0 means it will be skipped (info from MAME's source, matches the real hardware):

Horizontal shrink effect on a multicolored tile, showing how pixels are skipped.

0: 0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0 (15 pixel skipped, 1 remaining)
1: 0,0,0,0,1,0,0,0,1,0,0,0,0,0,0,0 (14 pixels skipped...)
2: 0,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0
3: 0,0,1,0,1,0,0,0,1,0,0,0,1,0,0,0
4: 0,0,1,0,1,0,0,0,1,0,0,0,1,0,1,0
5: 0,0,1,0,1,0,1,0,1,0,0,0,1,0,1,0
6: 0,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0
7: 1,0,1,0,1,0,1,0,1,0,1,0,1,0,1,0
8: 1,0,1,0,1,0,1,0,1,1,1,0,1,0,1,0
9: 1,0,1,1,1,0,1,0,1,1,1,0,1,0,1,0
A: 1,0,1,1,1,0,1,0,1,1,1,0,1,0,1,1
B: 1,0,1,1,1,0,1,1,1,1,1,0,1,0,1,1
C: 1,0,1,1,1,0,1,1,1,1,1,0,1,1,1,1
D: 1,1,1,1,1,0,1,1,1,1,1,0,1,1,1,1
E: 1,1,1,1,1,0,1,1,1,1,1,1,1,1,1,1 (...1 pixel skipped)
F: 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1 (no pixels skipped, full size)

Centering

Centering can be required since the "anchor point" of sprites is fixed at their top left corner.

Todo: code example.

@@ Line 1: / Line 1: @@
-Shrinking (also known as scaling, reduction, zooming...) is a hardware feature of the NeoGeo that reduces the sprites sizes with per-pixel accuracy.
+Shrinking (also known as scaling, reduction, and "zooming") is a hardware feature of the NeoGeo which allows to scale down [[sprites]] with per-pixel accuracy in both dimensions.
-It can be seen as subsampling of the original graphics, there's no smooth interpolation at all.
+Shrinking is performed by [[LSPC]] by skipping a variable number of pixel lines or columns. It can be seen as a simple subsampling of the original graphics since there's no smoothing applied at all.
 =Vertical shrinking=
-To do. See [[Sprites]].
+The vertical shrinking is set by an 8-bit value specifying the final height of the sprite's '''graphics'''. This value is set in [[VRAM]], in the [[Sprites|SCB2]].
-Range: $FF is full size, $0 is smallest.
+Range: $FF is the tallest, $0 is the smallest.
-Sprite set to height = 4, graphics intentionally filling 4 tiles (magenta representing size):
+To know which line to skip, LSPC uses a lookup table stored in the {{Chipname|L0 ROM}}.
-[[File:spritez_4.png]]
-If the same sprite is updated to be only 3 tiles high (magenta representing size) without cleaning:
+The vertical shrink parameter propagates in [[Sticky bit|chained sprites]].
-[[File:spritez_3.png]]
-It will shrink this way, showing the garbage yellow tile from the previous setup:
+==Caveat: Display window==
-[[File:spritez_anim.gif]]
+Note that vertical shrinking does not affect the tile height setting of the sprite. The graphics are shrunk '''inside''' the defined window.
+<gallery>
+File:spritez_4.png|Sprite height set to 4 tiles, graphics intentionally filling 4 tiles
+File:spritez_3.png|The same sprite updated to be only 3 tiles high without clearing the 4th (yellow) tile
+File:spritez_anim.gif|The sprite will shrink this way, showing the garbage yellow tile from the previous setup
+</gallery>
+==Caveat: Last line repeat==
+If the display window of a sprite is taller than the shrunk graphics, the remaining lines will be filled with repeats of the last line of the last tile (the bottom line of the tile at map index 15).
+SNK recommends leaving that line fully transparent if this causes problems.
 =Horizontal shrinking=
-The horizontal shrinking value is a 4-bit value indicating the final width of the sprite +1 (giving 1 to 16 pixels wide sprites). This value is also set in [[VRAM]], in the [[Sprites|SCB2]].
+The horizontal shrinking is set by a 4-bit value specifying the final width of the sprite graphics +1 (giving 1 to 16 pixels wide sprites). This value is also set in [[Sprites|SCB2]].
-Range: $F is full size, $0 is 1 pixel wide.
+Range: $F is full size (all 16 pixels shown), $0 is the smallest (only 1 pixel shown).
-Skipping of the pixels to render the effect is done by a hardwired lookup table in the [[GPU]]. This table is '''not''' in the [[LO ROM]].
+The horizontal shrink parameter does '''not''' propagate in chained sprites. Values for each sprite of a group [[Scaling sprite groups|have to be distributed]] to obtain the total desired group width.
-For each shrinking value, 1 means the pixel will be drawn, 0 means it will be skipped (info from MAME's source, matches the real hardware):
+There is no external lookup table for horizontal shrinking. The process is completely done inside LSPC.
+In the following table, each line corresponds to a shrinking value. 1 means the pixel will be drawn and 0 means it will be skipped (info from MAME's source, matches the real hardware):
-[[File:Hshrink.gif|thumb]]
+[[File:Hshrink.gif|thumb|Horizontal shrink effect on a multicolored tile, showing how pixels are skipped.]]
-*0: 0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0 (1 pixel skipped)
+*0: 0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0 (15 pixel skipped, 1 remaining)
-*1: 0,0,0,0,1,0,0,0,1,0,0,0,0,0,0,0
+*1: 0,0,0,0,1,0,0,0,1,0,0,0,0,0,0,0 (14 pixels skipped...)
 *2: 0,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0
 *3: 0,0,1,0,1,0,0,0,1,0,0,0,1,0,0,0
@@ Line 44: / Line 56: @@
 *C: 1,0,1,1,1,0,1,1,1,1,1,0,1,1,1,1
 *D: 1,1,1,1,1,0,1,1,1,1,1,0,1,1,1,1
-*E: 1,1,1,1,1,0,1,1,1,1,1,1,1,1,1,1
+*E: 1,1,1,1,1,0,1,1,1,1,1,1,1,1,1,1 (...1 pixel skipped)
 *F: 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1 (no pixels skipped, full size)
-==Table logic==
+=Centering=
-The lookup table might not be a real ROM table but a logic function.
+Centering can be required since the "anchor point" of sprites is fixed at their top left corner.
-For each pixel of the line, WXYZ being the reduction value:
+Todo: code example.
-*0 = W(X+Y)
-*1 = W+X
-*2 = WX
-*3 = W+X+Y
-*4 = WXY
-*5 = W+(XY)
-*6 = W
-*7 = 1
-*8 = WX+WYZ
-*9 = W+X(Y+Z)
-*A = WXYZ
-*B = W+X+Y+Z
-*C = W(X+Y+Z)
-*D = W+X+(YZ)
-*E = WX(Y+Z)
-*F = W+(XYZ)
 [[Category:Video system]]

Sprite shrinking: Difference between revisions