Difference between revisions of "Sprites Transparency Index Register"
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(Created page with "{{NextRegister |Number=$4B |Readable=Yes |Writable=Yes |ShortDesc=Index into sprite palette (of "transparent" colour). }} Index into sprite palette, set to $E3 after reset....") |
(Added extra info about 4-bit transparency from forum post.) |
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When rendering sprites, the pixel index is compared before palette-offset (byte 3 of {{PortNo|$xx57}}) is applied to it. The transparency is index-based, not colour based (contrary to Layer 2/ULA/LoRes modes, where resulting pixel colour is compared). | When rendering sprites, the pixel index is compared before palette-offset (byte 3 of {{PortNo|$xx57}}) is applied to it. The transparency is index-based, not colour based (contrary to Layer 2/ULA/LoRes modes, where resulting pixel colour is compared). | ||
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| + | The 4-bit sprite compares pixel-index to low 4 bits of this register, i.e. 4-bit pixel $3 (%0011) is treated as transparent, if this register still contains default $E3 (%1110_0011) value. | ||
Revision as of 13:34, 21 December 2018
| Number | $4B |
|---|---|
| Readable | Yes |
| Writable | Yes |
| Short Description | Index into sprite palette (of "transparent" colour). |
Index into sprite palette, set to $E3 after reset.
When rendering sprites, the pixel index is compared before palette-offset (byte 3 of Sprite Attribute Upload ($xx57 / 87)) is applied to it. The transparency is index-based, not colour based (contrary to Layer 2/ULA/LoRes modes, where resulting pixel colour is compared).
The 4-bit sprite compares pixel-index to low 4 bits of this register, i.e. 4-bit pixel $3 (%0011) is treated as transparent, if this register still contains default $E3 (%1110_0011) value.