Implemented OAM, SAT so sprites and background scrolling now work
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@@ -117,6 +117,7 @@ namespace Core.Video
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_statusRegister |= 0x80; // Set Bit 7 (VBlank Flag) to 1
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RenderBackground(); // <--- DRAW THE FRAME!
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RenderSprites();
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}
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// End of the NTSC frame (262 lines)
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@@ -129,62 +130,148 @@ namespace Core.Video
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private void RenderBackground()
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{
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// The Name Table base address is stored in VDP Register 2.
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// It tells us where in VRAM the 32x24 screen grid starts.
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ushort nameTableBase = (ushort)((Registers[2] & 0x0E) << 10);
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// Loop through all 24 rows and 32 columns of the screen
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for (int row = 0; row < 24; row++)
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byte scrollX = Registers[8];
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byte scrollY = Registers[9];
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bool lockRowScroll = (Registers[0] & 0x80) != 0; // Top 2 rows (Y < 16)
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bool lockColScroll = (Registers[0] & 0x40) != 0; // Right 8 columns (X >= 192)
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for (int screenY = 0; screenY < 192; screenY++)
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{
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for (int col = 0; col < 32; col++)
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for (int screenX = 0; screenX < 256; screenX++)
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{
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// Apply Vertical Scrolling (Depends on X for column locking!)
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int effectiveScrollY = scrollY;
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if (lockColScroll && screenX >= 192) effectiveScrollY = 0;
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int vdpY = (screenY + effectiveScrollY) % 224;
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int row = vdpY / 8;
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int tileY = vdpY % 8;
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// Apply Horizontal Scrolling (Depends on Y for row locking!)
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int effectiveScrollX = scrollX;
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if (lockRowScroll && screenY < 16) effectiveScrollX = 0;
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int vdpX = (screenX - effectiveScrollX) & 0xFF;
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int col = vdpX / 8;
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int tileX = vdpX % 8;
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// 1. Read the 16-bit Tile instruction from the Name Table
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ushort nameTableAddr = (ushort)(nameTableBase + (row * 64) + (col * 2));
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byte lowByte = VRAM[nameTableAddr];
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byte highByte = VRAM[nameTableAddr + 1];
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ushort tileData = (ushort)((highByte << 8) | lowByte);
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// 2. Extract the Tile Index and Palette Info
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// 2. Extract Tile Index and Palette Info
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int tileIndex = tileData & 0x01FF;
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bool useSpritePalette = (tileData & 0x0800) != 0;
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// 3. Find the actual pixel data for this tile in VRAM
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// Each 8x8 tile takes exactly 32 bytes in memory
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// 3. Find the tile data in VRAM
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ushort tileAddress = (ushort)(tileIndex * 32);
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// 4. Draw the 8x8 block of pixels!
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for (int y = 0; y < 8; y++)
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// 4. Fetch the 4 bitplanes
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byte bp0 = VRAM[tileAddress + (tileY * 4) + 0];
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byte bp1 = VRAM[tileAddress + (tileY * 4) + 1];
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byte bp2 = VRAM[tileAddress + (tileY * 4) + 2];
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byte bp3 = VRAM[tileAddress + (tileY * 4) + 3];
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// 5. Extract color index
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int shift = 7 - tileX;
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int colorIndex = ((bp0 >> shift) & 1) |
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(((bp1 >> shift) & 1) << 1) |
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(((bp2 >> shift) & 1) << 2) |
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(((bp3 >> shift) & 1) << 3);
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int paletteOffset = useSpritePalette ? 16 : 0;
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byte smsColor = CRAM[paletteOffset + colorIndex];
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int r = (smsColor & 0x03) * 85;
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int g = ((smsColor >> 2) & 0x03) * 85;
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int b = ((smsColor >> 4) & 0x03) * 85;
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FrameBuffer[(screenY * 256) + screenX] = (255 << 24) | (r << 16) | (g << 8) | b;
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}
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}
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}
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private void RenderSprites()
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{
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// 1. Find the Sprite Attribute Table (SAT)
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// Register 5 contains the base address bits (Mask 0x7E, shifted by 7)
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ushort satBaseAddress = (ushort)((Registers[5] & 0x7E) << 7);
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// 2. Register 6 determines where the Sprite Tile graphics are stored in VRAM
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ushort spritePatternBase = (ushort)((Registers[6] & 0x04) << 11);
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// 3. Register 1 determines sprite size (8x8 or 8x16)
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bool is8x16 = (Registers[1] & 0x02) != 0;
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// The SMS can draw a maximum of 64 sprites
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for (int i = 0; i < 64; i++)
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{
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// Read the Y coordinate from the first part of the SAT
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byte y = VRAM[satBaseAddress + i];
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// HARDWARE QUIRK: If Y == 208 in standard 192-line mode,
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// it acts as a "Stop Drawing" marker. The VDP aborts the rest of the list!
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if (y == 208) break;
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// The X coordinates and Tile Indices are interleaved starting at SAT + 0x80
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byte x = VRAM[satBaseAddress + 0x80 + (i * 2)];
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byte tileIndex = VRAM[satBaseAddress + 0x80 + (i * 2) + 1];
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// If sprites are 8x16, the Tile Index always drops the lowest bit (forces even alignment)
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if (is8x16) tileIndex = (byte)(tileIndex & 0xFE);
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// Calculate the pixel height for the drawing loop
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int spriteHeight = is8x16 ? 16 : 8;
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// Draw the 8x8 (or 8x16) sprite block
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for (int py = 0; py < spriteHeight; py++)
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{
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// Master System Sprites are physically shifted down 1 pixel on the CRT
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int screenY = y + 1 + py;
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// If this row of the sprite is off the bottom of the screen, skip it
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if (screenY >= 192) continue;
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// Calculate where the 4 bitplanes are for this specific row of the sprite
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ushort tileAddress = (ushort)(spritePatternBase + (tileIndex * 32) + (py * 4));
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byte bp0 = VRAM[tileAddress + 0];
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byte bp1 = VRAM[tileAddress + 1];
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byte bp2 = VRAM[tileAddress + 2];
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byte bp3 = VRAM[tileAddress + 3];
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for (int px = 0; px < 8; px++)
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{
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// The SMS uses 4 bitplanes to make a single row of pixels.
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byte bp0 = VRAM[tileAddress + (y * 4) + 0];
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byte bp1 = VRAM[tileAddress + (y * 4) + 1];
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byte bp2 = VRAM[tileAddress + (y * 4) + 2];
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byte bp3 = VRAM[tileAddress + (y * 4) + 3];
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int screenX = x + px;
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for (int x = 0; x < 8; x++)
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{
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// Combine 1 bit from each bitplane to get a color index (0-15)
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int shift = 7 - x;
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int colorIndex = ((bp0 >> shift) & 1) |
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(((bp1 >> shift) & 1) << 1) |
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(((bp2 >> shift) & 1) << 2) |
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(((bp3 >> shift) & 1) << 3);
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// If this pixel is off the right side of the screen, skip it
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if (screenX >= 256) continue;
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// Find the raw SMS color in CRAM
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int paletteOffset = useSpritePalette ? 16 : 0;
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byte smsColor = CRAM[paletteOffset + colorIndex];
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int shift = 7 - px;
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int colorIndex = ((bp0 >> shift) & 1) |
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(((bp1 >> shift) & 1) << 1) |
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(((bp2 >> shift) & 1) << 2) |
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(((bp3 >> shift) & 1) << 3);
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// Translate SMS 00BBGGRR format to Windows 32-bit ARGB
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int r = (smsColor & 0x03) * 85;
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int g = ((smsColor >> 2) & 0x03) * 85;
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int b = ((smsColor >> 4) & 0x03) * 85;
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// HARDWARE TRANSPARENCY:
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// If the color index is 0, DO NOT draw it! Let the background show through.
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if (colorIndex == 0) continue;
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// Calculate where this pixel goes on the final 256x192 screen
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int pixelX = (col * 8) + x;
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int pixelY = (row * 8) + y;
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// Sprites ALWAYS use the second half of CRAM (Palette 1: Indices 16-31)
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byte smsColor = CRAM[16 + colorIndex];
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FrameBuffer[(pixelY * 256) + pixelX] = (255 << 24) | (r << 16) | (g << 8) | b;
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}
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int r = (smsColor & 0x03) * 85;
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int g = ((smsColor >> 2) & 0x03) * 85;
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int b = ((smsColor >> 4) & 0x03) * 85;
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// Because we only draw non-zero pixels, this safely overwrites the
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// background FrameBuffer exactly where the sprite stands!
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FrameBuffer[(screenY * 256) + screenX] = (255 << 24) | (r << 16) | (g << 8) | b;
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}
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}
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}
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