Add files

.gitignore

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+build/
+*.2bpp

.gitmodules

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+[submodule "mgblib"]
+	path = mgblib
+	url = https://github.com/mattcurrie/mgblib

Makefile

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+SRCDIR   = src
+OBJDIR   = build
+IMAGE_DEPS = img/footer.2bpp
+
+SOURCES  := $(wildcard $(SRCDIR)/*.asm)
+OBJECTS  := $(SOURCES:$(SRCDIR)/%.asm=$(OBJDIR)/%.o)
+ROMS  := $(SOURCES:$(SRCDIR)/%.asm=$(OBJDIR)/%.gb)
+
+all: $(OBJDIR) $(ROMS)
+
+%.2bpp: %.png
+	rgbgfx -o $@ $<
+
+$(OBJDIR):
+	@echo "Creating $(directory)..."
+	mkdir -p $@
+
+$(ROMS): $(OBJDIR)/%.gb : $(OBJDIR)/%.o
+	rgblink -n $(basename $@).sym -m $(basename $@).map -o $@ $<
+	rgbfix -t "DMG-ACID2" -v -p 255 $@
+
+-include $(OBJECTS:.o=.d)
+
+$(OBJECTS): $(OBJDIR)/%.o : $(SRCDIR)/%.asm $(IMAGE_DEPS)
+	rgbasm -i mgblib/ -M $(OBJDIR)/$*.d -o $@ $<
+
+.PHONY: clean
+clean:
+	rm -rf $(OBJDIR)
+	rm img/*.2bpp

README.md

@@ -1,2 +1,148 @@
 # dmg-acid2
-  😀 The Acid2 test, now for Game Boy! 😀
+dmg-acid2 is a test for developers of Game Boy (DMG) emulators to verify their
+emulation of the Game Boy's Pixel Processing Unit (PPU).
+
+[Download the ROM](https://github.com/mattcurrie/dmg-acid2/releases/download/v1.0/dmg-acid2.gb),
+or build using [RGBDS](https://github.com/rednex/rgbds):
+
+```
+git clone --recurse-submodules https://github.com/mattcurrie/dmg-acid2
+cd dmg-acid2 && make
+```
+
+For testing the Game Boy Color you can try [cgb-acid2](https://github.com/mattcurrie/cgb-acid2).
+
+## Reference Image
+An accurate DMG emulator should generate output identical to the image below:
+
+![reference image](img/reference-dmg.png)
+
+An accurate CGB emulator running in DMG mode should generate output identical
+to the image below:
+
+![reference image](img/reference-cgb.png)
+
+A DMG emulator should use these 8-bit values in greyscale images or in RGB
+components to ensure the images can be compared correctly: 
+`$00`, `$55`, `$AA`, `$FF`.
+
+When emulating a CGB running in DMG mode, you should use this formula to
+convert each 5-bit CGB palette component to 8-bit: 
+`(r << 3) | (r >> 2)`
+
+[Reference photo from DMG](https://github.com/mattcurrie/dmg-acid2/raw/master/img/photo-dmg.jpg) 
+[Reference photo from CGB](https://github.com/mattcurrie/dmg-acid2/raw/master/img/photo-cgb.jpg)
+
+## Emulator Requirements
+A simple line based renderer is sufficient to generate the correct output. This
+is NOT a [PPU timing torture test requiring T-cycle accuracy](https://github.com/mattcurrie/mealybug-tearoom-tests),
+and does NOT perform register writes during the PPU's mode 3.
+
+The test uses LY=LYC coincidence interrupts to perform register writes on
+specific rows of the screen during mode 2 (OAM scan).
+
+## Guide
+
+### Hello World!
+The "Hello World" text is constructed from 10 objects, and the exclaimation
+mark is part of the background. There is also an additional solid white object
+where the exclaimation mark is. Due to the 10 object per line limit, the solid
+white object should not be drawn, allowing the background to show through.
+
+### Hair
+The mohawk hair is not visible in the reference image. The hair tiles are 
+part of the background. For rows 8-15, bit 0 of LCDC is reset, so the
+background should not be displayed, and instead color 0 from BGP should be
+drawn on the screen.
+
+### Eyes
+The eyes consist of four background/window tiles, and objects overlapping color
+0 background pixels.
+
+The left eye is drawn using the background, and the right eye is drawn using
+the window (and also the right edge of the head beside the right eye). At the
+bottom of the eye, the WX register is set to an off-screen value, so the window
+is hidden until the WX register is set again for drawing the right side of the
+chin.
+
+The background/window tiles for the left half of both eyes have color 0 for the
+pupil region of the eye. There are two dark grey colored objects that overlap
+the left half of both eyes that have the OBJ-to-BG Priority (bit 7) set in the
+OAM flags, so the object will only show through color 0 of the background/
+window tile and replaces the white color.
+
+The top half of each eye uses tile data from the $8000-8fff region of VRAM. The
+bottom half of each eye uses tile data from the $8800-97ff region of VRAM. 
+The bottom half of the eye uses tiles with index $a1 and $a2 to test that
+signed tile indexes are displayed correctly.
+
+### Moles
+The moles are not visible in the reference image, but can be seen in the
+failure case images.
+
+The mole beside the left eye is visible if the background tile data is read 
+from $8000-8fff instead of $8800-97ff.
+
+The mole left of the nose is not visible because a blank object with a lower
+X-coordinate has priority, even though it is defined later in OAM than the mole
+object.
+
+The mole right of the nose is not visible because a blank object at the same X
+coordinate has priority because it occurs earlier in OAM than the mole object.
+
+### Nose
+The nose consists of four objects using the same tile data that is flipped
+vertically and/or horizontally. The top left corner of the nose contains the
+unflipped tile.
+
+### Mouth
+The mouth consists of eight 8x16 objects. The left and right edges of the mouth
+contain unflipped tile data, and other objects use vertically flipped tile
+data.
+
+For the left side of the mouth, the objects specify tile index 12, and the right
+side of the mouth specify tile index 13. Because bit 0 of the tile index is
+ignored for 8x16 objects, the whole mouth effectively uses tile index 12.
+
+### Chin
+The right side of the chin is drawn using the window. After the right eye was
+drawn, the window was hidden by setting WX to an off-screen value. For the
+right side of the chin, the WX value is restored to an on-screen value. After
+the chin has been drawn, the window is disabled using bit 5 of the LCDC
+register so the window does not cover the footer text.
+
+For the right side of the chin, the window has been updated to use the tile map
+from the VRAM beginning at $9800.  Because 16 rows of window have already been
+drawn for the eye, the right side of the chin is rendered starting from address
+$9840.
+
+### Footer Text
+For the footer text, the background is set to use the $9c00-9fff region for
+the map data, and tile data is set to come from the $8800-97ff region.
+
+## Failure Examples
+See the table below for some examples of incorrect behaviour and the
+corresponding attribute/flag. This is not intended to be an exhaustive list of
+all possible failures.
+
+| Failure Example | Failure Description | Functionality Tested |
+| --------------- | ------------------- | -------------------- |
+| ![failure image](img/failures/obj-palette.png) | Nose missing | Object Palette (bit 4) |
+| ![failure image](img/failures/obj-horizontal-flip.png) | Nose tiles flipped, right eyelash flipped | Object Horizontal Flip (bit 5) |
+| ![failure image](img/failures/obj-vertical-flip.png) | Nose tiles filpped, mouth straight, eye whites bottom left wrong | Object Vertical Flip (bit 6) |
+| ![failure image](img/failures/obj-to-bg-priority.png) | Eye whites left half wrong | Object to Background Priority (bit 7) |
+| ![failure image](img/failures/bg-enable.png) | Hair visible | Background Enable (bit 0) |
+| ![failure image](img/failures/obj-enable.png) | Tongue visible | Object Enable (bit 1) |
+| ![failure image](img/failures/obj-size.png) | Half of mouth missing | Object Size (bit 2) |
+| ![failure image](img/failures/bg-map.png) | Footer missing | Background Tile Map (bit 3) |
+| ![failure image](img/failures/tile-sel.png) | Eye whites top left quadrant wrong | Background/Window Tile Data (bit 4) |
+| ![failure image](img/failures/win-enable.png) | Half of footer missing | Window Enable (bit 5) |
+| ![failure image](img/failures/win-map.png) | Right chin missing | Window Tile Map (bit 6) |
+| ![failure image](img/failures/obj-priority-lower-x.png) | Left mole visible | Object Priority Lower X Coordinate |
+| ![failure image](img/failures/obj-priority-same-x.png) | Right mole visible | Object Priority Same X Coordinate |
+| ![failure image](img/failures/10-obj-limit.png) | Hello World missing exclaimation mark (!) | 10 object per line limit |
+| ![failure image](img/failures/8x16-obj-tile-index-bit-0.png) | Half of mouth missing | Bit 0 of tile index for 8x16 objects should be ignored |
+
+## Credits
+Håkon Wium Lie and Ian Hickson for creation of the original 
+[Acid2](http://www.acidtests.org/) web standards compliance test.

inc/background.asm

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+BackgroundMap::
+    db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, "!", 0, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+    db 0, 0, 0, 0, 0, 0, 0, 0, 0, $10, $10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+    db 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+    db 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 2, 2, 1, 1, 0, 0, 0, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+    db 0, 0, 0, 0, 0, 1, 2, 2, 2, 2, 2, 2, 2, 2, 1, 0, 0, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+    db 0, 0, 0, 0, 1, 2, 2, 3, $a0, 2, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+    db 0, 0, 0, 0, 1, 9, 2, $a1, $a2, 2, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+    db 0, 0, 0, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+    db 0, 0, 0, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+    db 0, 0, 0, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+    db 0, 0, 0, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+    db 0, 0, 0, 0, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 0, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+    db 0, 0, 0, 0, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 0, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+    db 0, 0, 0, 0, 0, 1, 2, 2, 2, 2, 2, 2, 2, 2, 1, 0, 0, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+    db 0, 0, 0, 0, 0, 0, 1, 1, 2, 2, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+    db 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
+.end:

inc/oam.asm

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+OAMData::
+    ; nose - use OBP1 palette
+    db $50, $50, $4, $10
+    db $50, $58, $4, $30
+    db $58, $50, $4, $50
+    db $58, $58, $4, $70
+
+    ; left eye - overlapping background color 0 only, so fills in the whites of the eyes
+    db $38, $40, $a3, $90
+    db $40, $40, $a3, $d0
+
+    ; right eye - overlapping window color 0 only, so fills in the whites of the eyes
+    db $38, $60, $a3, $90
+    db $40, $60, $a3, $d0
+
+    ; hello world
+    db $10, $28, "H", 0
+    db $10, $30, "e", 0
+    db $10, $38, "l", 0
+    db $10, $40, "l", 0
+    db $10, $48, "o", 0
+
+    db $10, $58, "W", 0
+    db $10, $60, "o", 0
+    db $10, $68, "r", 0
+    db $10, $70, "l", 0
+    db $10, $78, "d", 0
+    db $10, $80, 1, $10       ; this solid white box shouldn't display - 10 sprite limit per line
+
+    ; mouth
+    db $68, $38, 12, $00     ; sprite size is 8x16 when these sprites are rendered
+    db $68, $40, 12, $40     ; y-flipped 8x16 sprite
+    db $68, $48, 12, $40
+    db $68, $50, 12, $40
+    db $68, $58, 13, $40     ; specify tile 13, but bit 0 of tile index is ignored in 8x16 tile mode
+    db $68, $60, 13, $40
+    db $68, $68, 13, $40
+    db $68, $70, 13, $00
+
+
+    db $52, $3d, 9, $00     ; mole
+    db $52, $3c, 10, $00    ; light grey square - lower x-coordinate so has priority over the mole
+                            ; even though the mole has a lower index in OAM
+
+    db $52, $6c, 10, $00    ; light grey square - same x-coordinate so tile with lower index in OAM
+                            ; has priority
+    db $52, $6c, 9, $00     ; mole
+
+    
+    db $38, $3a, 5, $00     ; left eyelash top
+    db $40, $3a, 6, $00     ; left eyelash bottom
+    
+    db $38, $6e, 5, $20     ; right eyelash top
+    db $40, $6e, 6, $20     ; right eyelash bottom
+
+    db $78, $54, 15, $00    ; tongue
+.end: