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Ensures only the first 8px of sprites is output in 8x8 mode.

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Also adds a little extra documentation.
This commit is contained in:
Thomas Harte 2018-07-15 22:21:29 -04:00
parent e339d169c5
commit 92065813ef
1 changed files with 25 additions and 8 deletions
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33
Components/9918/9918.cpp
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@ -496,17 +496,25 @@ void TMS9918::run_for(const HalfCycles cycles) {
} }
} }
// Paint sprites and check for collisions. // Paint sprites and check for collisions, but only if at least one sprite is active
// on this line.
if(sprite_set.active_sprite_slot) { if(sprite_set.active_sprite_slot) {
int sprite_pixels_left = pixels_left; int sprite_pixels_left = pixels_left;
const int shift_advance = sprites_magnified_ ? 1 : 2; const int shift_advance = sprites_magnified_ ? 1 : 2;
const uint32_t sprite_colour_selection_masks[2] = {0x00000000, 0xffffffff}; static const uint32_t sprite_colour_selection_masks[2] = {0x00000000, 0xffffffff};
const int colour_masks[16] = {0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1}; static const int colour_masks[16] = {0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1};
while(sprite_pixels_left--) { while(sprite_pixels_left--) {
// sprite_colour is the colour that's going to reach the display after sprite logic has been
// applied; by default assume that nothing is going to be drawn.
uint32_t sprite_colour = pixel_base_[output_column_ - first_pixel_column_]; uint32_t sprite_colour = pixel_base_[output_column_ - first_pixel_column_];
// The sprite_mask is used to keep track of whether two sprites have both sought to output
// a pixel at the same location, and to feed that into the status register's sprite
// collision bit.
int sprite_mask = 0; int sprite_mask = 0;
int c = sprite_set.active_sprite_slot; int c = sprite_set.active_sprite_slot;
while(c--) { while(c--) {
SpriteSet::ActiveSprite &sprite = sprite_set.active_sprites[c]; SpriteSet::ActiveSprite &sprite = sprite_set.active_sprites[c];
@ -517,15 +525,24 @@ void TMS9918::run_for(const HalfCycles cycles) {
} else if(sprite.shift_position < 32) { } else if(sprite.shift_position < 32) {
int mask = sprite.image[sprite.shift_position >> 4] << ((sprite.shift_position&15) >> 1); int mask = sprite.image[sprite.shift_position >> 4] << ((sprite.shift_position&15) >> 1);
mask = (mask >> 7) & 1; mask = (mask >> 7) & 1;
status_ |= (mask & sprite_mask) << StatusSpriteCollisionShift;
sprite_mask |= mask;
sprite.shift_position += shift_advance;
mask &= colour_masks[sprite.info[3]&15]; // Ignore the right half of whatever was collected if sprites are not in 16x16 mode.
sprite_colour = (sprite_colour & sprite_colour_selection_masks[mask^1]) | (palette[sprite.info[3]&15] & sprite_colour_selection_masks[mask]); if(sprite.shift_position < (sprites_16x16_ ? 32 : 16)) {
// If any previous sprite has been painted in this column and this sprite
// has this pixel set, set the sprite collision status bit.
status_ |= (mask & sprite_mask) << StatusSpriteCollisionShift;
sprite_mask |= mask;
// Check that the sprite colour is not transparent
mask &= colour_masks[sprite.info[3]&15];
sprite_colour = (sprite_colour & sprite_colour_selection_masks[mask^1]) | (palette[sprite.info[3]&15] & sprite_colour_selection_masks[mask]);
}
sprite.shift_position += shift_advance;
} }
} }
// Output whichever sprite colour was on top.
pixel_base_[output_column_ - first_pixel_column_] = sprite_colour; pixel_base_[output_column_ - first_pixel_column_] = sprite_colour;
output_column_++; output_column_++;
} }