Auto animation: Difference between revisions

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[[File:Autoanim.gif|frame|2bit (4 tiles) example from [[Mutation Nation]]]]
[[File:Autoanim.gif|frame|2bit (4 tiles) example from [[Mutation Nation]].]]


(Information from [[Charles MacDonald]])
Some information from Charles MacDonald.


Auto-animation is a tile attribute for [[sprites]] and a special feature of the GPU used to animate loops without CPU usage.
Auto-animation is a special feature of the video controller allowing animation of simple loops with no CPU usage. It is enabled via [[sprites|sprite]] tile attributes bits.


An internal write-only 8bit counter is automatically decremented each frame. When it underflows, it is reloaded with the last value written to it, which comes from the 8 highest bits of {{Reg|REG_LSPCMODE}}. This sets the speed of the animation.
==Usage==


Each time that counter underflows, another internal 3bit counter is incremented. Those 3 bits can only be read in bits 2~0 of REG_LSPCMODE.
The auto-animation speed is a global setting, which is set in the highest 8 bits of {{Reg|REG_LSPCMODE}}. A value of n will tick the animation every n+1 frames.


When auto-animation is disabled (bit 3 of REG_LSPCMODE set), the frame counter and animation counter continue to function. However, tiles are shown as if their animation mode select bits were reset (so the tile number specified is the tile shown).
When setting the auto-animation speed, the new value is only taken into account the next time the timer underflows (reloads), not immediately after the write.


These bits can be set in each tile's attribute word (odd bytes of [[Sprites|SCB1]]):
Bit 3 of REG_LSPCMODE stalls animation when set. The animation counter is '''read only''', from the lower 3 bits of REG_LSPCMODE.
{{16BitRegister|[[Palettes|Palette]]|8|Tile number MSBs|4|'''3bit auto-anim'''|1|'''2bit auto-anim'''|1|Vertical flip|1|Horizontal flip|1}}


Bit 3 has priority.
Auto-animation is enabled per-tile via 2 bits in the odd bytes of [[Sprites|SCB1]]:
{{16BitRegister|[[Palettes|Palette]]|8|Tile number MSBs|4|'''3-bit auto-anim'''|1|'''2-bit auto-anim'''|1|Vertical flip|1|Horizontal flip|1}}


Depending on the animation period (4 or 8 frames), the tile number specified in [[Sprites|SCB1]] has the lower 2 or 3 bits replaced with those of the animation counter.
Effects:


Note that the bits are replaced, not added. Therefore, the consecutive tiles used for animation must be aligned on 4 or 8.
{|class="wikitable"
!Bit 3||Bit 2||Effect
|-
|0||0||No auto-animation for this tile. Tile shown is the tile number.
|-
|0||1||Auto-animation over 4 tiles.
|-
|1||0||Auto-animation over 8 tiles.
|-
|1||1||Auto-animation over 8 tiles (bit 2 is ignored).
|}
 
Depending on the animation period (4 or 8 frames), the tile number specified in [[Sprites|SCB1]] has the lower 2 or 3 bits '''replaced''' with those of the animation counter.
 
Note that the bits are '''replaced''', not added. Therefore, the tiles must be carefully aligned to the right positions in the [[C ROM]]s.
 
==Operation==
 
An internal 8-bit timer is ticked each frame. When it underflows, two things happen:
 
* The timer is reloaded with the last value written to it, which comes from the 8 highest bits of REG_LSPCMODE.
* An internal 3-bit animation counter is incremented.
 
When auto-animation is disabled (bit 3 of REG_LSPCMODE set), the timer and animation counter continue to function. However, '''all''' tiles are shown as if their animation mode select bits were reset (so the tile number specified is the tile shown).


[[Category:Video system]]
[[Category:Video system]]

Latest revision as of 01:52, 27 February 2018

2bit (4 tiles) example from Mutation Nation.

Some information from Charles MacDonald.

Auto-animation is a special feature of the video controller allowing animation of simple loops with no CPU usage. It is enabled via sprite tile attributes bits.

Usage

The auto-animation speed is a global setting, which is set in the highest 8 bits of REG_LSPCMODE. A value of n will tick the animation every n+1 frames.

When setting the auto-animation speed, the new value is only taken into account the next time the timer underflows (reloads), not immediately after the write.

Bit 3 of REG_LSPCMODE stalls animation when set. The animation counter is read only, from the lower 3 bits of REG_LSPCMODE.

Auto-animation is enabled per-tile via 2 bits in the odd bytes of SCB1:

Bit 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Def Palette Tile number MSBs3-bit auto-anim2-bit auto-animVertical flipHorizontal flip

Effects:

Bit 3 Bit 2 Effect
0 0 No auto-animation for this tile. Tile shown is the tile number.
0 1 Auto-animation over 4 tiles.
1 0 Auto-animation over 8 tiles.
1 1 Auto-animation over 8 tiles (bit 2 is ignored).

Depending on the animation period (4 or 8 frames), the tile number specified in SCB1 has the lower 2 or 3 bits replaced with those of the animation counter.

Note that the bits are replaced, not added. Therefore, the tiles must be carefully aligned to the right positions in the C ROMs.

Operation

An internal 8-bit timer is ticked each frame. When it underflows, two things happen:

  • The timer is reloaded with the last value written to it, which comes from the 8 highest bits of REG_LSPCMODE.
  • An internal 3-bit animation counter is incremented.

When auto-animation is disabled (bit 3 of REG_LSPCMODE set), the timer and animation counter continue to function. However, all tiles are shown as if their animation mode select bits were reset (so the tile number specified is the tile shown).

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