/// <summary>
/// Reconstructs the sprite info table from OAM.
/// </summary>
public void ReconstructOAMTable()
{
for (int i = 0; i < SpriteInfoTable.Length; i++)
{
int off = i << 2;
SpriteInfoTable[i].OAMIndex = off;
SpriteInfoTable[i].YOffset = OAM[off + 0] - 16;
SpriteInfoTable[i].XOffset = OAM[off + 1] - 8;
SpriteInfoTable[i].TileOffset = OAM[off + 2] << 4;//index * 16 = offset in VRAM of tile
SpriteInfoTable[i].SpriteProperties = OAM[off + 3];
// Sprites are sorted by their X position. In the case that their Xs are equal,
// the one with the lower OAM position takes priority. Because they are already
// 'sorted by OAM offset', only Xs need to be compared.
int x = i;
while (x > 0 && (SpriteInfoTable[x].XOffset < SpriteInfoTable[x - 1].XOffset))
{
SpriteInfo temp = SpriteInfoTable[x - 1];
SpriteInfoTable[x - 1] = SpriteInfoTable[x];
SpriteInfoTable[x] = temp;
x--;
}
}
for (int i = 0; i < SpritesOnScanline.Length; i++)
{
SpritesOnScanline[i] = new SpriteInfo()
{
OAMIndex = int.MaxValue,
XOffset = int.MaxValue,
YOffset = int.MaxValue
};
}
}
/// <summary>
/// Draws the sprites on the current scanline.
/// </summary>
private void DrawSpriteScanline()
{
int LineSpriteCount = 0;
for (int i = 0; i < SpriteInfoTable.Length; i++)
{
SpriteInfo currentSprite = SpriteInfoTable[i];
// Only draw if the sprite is on the scanline
if (LY >= currentSprite.YOffset && LY < currentSprite.YOffset + SpriteHeight)
{
LineSpriteCount++;
if (!currentSprite.IsOnScreen)
{
continue;
}
int SpritePixelY = LY - currentSprite.YOffset;
int SpriteTileOffset = 0;
if (Sprite8By16Mode)
{
if (SpritePixelY < 8)
{
SpriteTileOffset = currentSprite.UpperTileOffset;
}
else
{
SpritePixelY -= 8;
SpriteTileOffset = currentSprite.LowerTileOffset;
}
}
else
{
SpriteTileOffset = currentSprite.TileOffset;
}
for (int LCD_X = currentSprite.XOffset, SpritePixelX = 0; LCD_X < currentSprite.XOffset + 8; LCD_X++, SpritePixelX++)
{
if (LCD_X >= LCDWidth)
{
break;
}
int SpriteColorNum = GetPixelPaletteNumberFromTile(SpriteTileOffset, SpritePixelX, SpritePixelY, currentSprite.XFlip, currentSprite.YFlip);
// Color 0 is never drawn (transparent).
// If PriorityOverBG, sprite pixel is drawn over BG, except in the case of sprite color 0.
// If !PriorityOverBG, sprite pixel isn't drawn over BG, except when BG color is 0.
if (SpriteColorNum == 0)
{
continue;
}
bool PriorityOverExistingSprite = (currentSprite.XOffset < SpritesOnScanline[LCD_X].XOffset) || (currentSprite.OAMIndex < SpritesOnScanline[LCD_X].OAMIndex);
if (PriorityOverExistingSprite && (currentSprite.PriorityOverBG || BackgroundColorNumOnScanline[LCD_X] == 0))
{
SetPixel(LCD_X, LY, DMGObjectPalettes[currentSprite.DMGObjectPaletteNum][SpriteColorNum]);
SpritesOnScanline[LCD_X] = currentSprite;
}
}
}
if (LineSpriteCount >= 10)
{
break;
}
}
}
