EightBit/LR35902/src/Display.cpp

#include "stdafx.h"
#include "Display.h"
#include "Processor.h"
#include "CharacterDefinition.h"
#include "ObjectAttribute.h"

#include <vector>

EightBit::GameBoy::Display::Display(const AbstractColourPalette* colours, Bus& bus)
: m_bus(bus),
  m_colours(colours),
  m_control(0),
  m_scanLine(0) {
}

const std::vector<uint32_t>& EightBit::GameBoy::Display::pixels() const {
	return m_pixels;
}

void EightBit::GameBoy::Display::initialise() {
	m_pixels.resize(RasterWidth * RasterHeight);
}

void EightBit::GameBoy::Display::render() {
	m_scanLine = m_bus.peekRegister(Bus::LY);
	if (m_scanLine < RasterHeight) {
		m_control = m_bus.peekRegister(Bus::LCDC);
		if (m_control & Bus::LcdEnable) {
			if (m_control & Bus::DisplayBackground)
				renderBackground();
			if (m_control & Bus::ObjectEnable)
				renderObjects();
		}
	}
}

std::array<int, 4> EightBit::GameBoy::Display::createPalette(const int address) {
	const auto raw = m_bus.peekRegister(address);
	std::array<int, 4> palette;
	palette[0] = raw & 0b11;
	palette[1] = (raw & 0b1100) >> 2;
	palette[2] = (raw & 0b110000) >> 4;
	palette[3] = (raw & 0b11000000) >> 6;
	return palette;
}

void EightBit::GameBoy::Display::renderObjects() {
	const auto objBlockHeight = (m_control & Bus::ObjectBlockCompositionSelection) ? 16 : 8;
	renderObjects(objBlockHeight);
}

void EightBit::GameBoy::Display::loadObjectAttributes() {
	const auto objBlockHeight = (m_control & Bus::ObjectBlockCompositionSelection) ? 16 : 8;
	auto& oam = m_bus.OAMRAM();
	for (int i = 0; i < 40; ++i) {
		m_objectAttributes[i] = ObjectAttribute(oam, 4 * i, objBlockHeight);
	}
}

void EightBit::GameBoy::Display::renderObjects(int objBlockHeight) {
	
	std::vector<std::array<int, 4>> palettes(2);
	palettes[0] = createPalette(Bus::OBP0);
	palettes[1] = createPalette(Bus::OBP1);

	auto& vram = m_bus.VRAM();

	for (int i = 0; i < 40; ++i) {

		const auto& current = m_objectAttributes[i];

		const auto spriteY = current.positionY();
		const auto drawY = spriteY - 16;

		if ((m_scanLine >= drawY) && (m_scanLine < (drawY + objBlockHeight))) {

			const auto spriteX = current.positionX();
			const auto drawX = spriteX - 8;

			const auto sprite = current.pattern();
			const auto definition = CharacterDefinition(&vram, 16 * sprite, objBlockHeight);
			const auto& palette = palettes[current.palette()];
			const auto flipX = current.flipX();
			const auto flipY = current.flipY();

			renderTile(
				objBlockHeight,
				drawX, drawY,
				flipX, flipY, true,
				palette,
				definition);
		}
	}
}

void EightBit::GameBoy::Display::renderBackground() {

	auto palette = createPalette(Bus::BGP);

	const auto window = (m_control & Bus::WindowEnable) != 0;
	const auto bgArea = (m_control & Bus::BackgroundCodeAreaSelection) ? 0x1c00 : 0x1800;
	const auto bgCharacters = (m_control & Bus::BackgroundCharacterDataSelection) ? 0 : 0x800;

	const auto wx = m_bus.peekRegister(Bus::WX);
	const auto wy = m_bus.peekRegister(Bus::WY);

	const auto offsetX = window ? wx - 7 : 0;
	const auto offsetY = window ? wy : 0;

	const auto scrollX = m_bus.peekRegister(Bus::SCX);
	const auto scrollY = m_bus.peekRegister(Bus::SCY);

	renderBackground(bgArea, bgCharacters, offsetX - scrollX, offsetY - scrollY, palette);
}

void EightBit::GameBoy::Display::renderBackground(
		int bgArea, int bgCharacters,
		int offsetX, int offsetY,
		const std::array<int, 4>& palette) {

	auto& vram = m_bus.VRAM();

	const int row = (m_scanLine - offsetY) / 8;
	const auto baseAddress = bgArea + row * BufferCharacterWidth;

	for (int column = 0; column < BufferCharacterWidth; ++column) {

		const auto address = baseAddress + column;
		const auto character = vram.peek(address);

		const auto definition = CharacterDefinition(&vram, bgCharacters + 16 * character, 8);
		renderTile(
			8,
			column * 8 + offsetX, row * 8 + offsetY,
			false, false, false,
			palette,
			definition);
	}
}

void EightBit::GameBoy::Display::renderTile(
		const int height,
		const int drawX, const int drawY,
		const bool flipX, const bool flipY, const bool allowTransparencies,
		const std::array<int, 4>& palette,
		const CharacterDefinition& definition) {

	const auto width = 8;

	const auto flipMaskX = width - 1;
	const auto flipMaskY = height - 1;

	const auto y = m_scanLine;

	auto cy = y - drawY;
	if (flipY)
		cy = ~cy & flipMaskY;

	const auto rowDefinition = definition.get(cy);

	const auto lineAddress = y * RasterWidth;
	for (int cx = 0; cx < width; ++cx) {

		const uint8_t x = drawX + (flipX ? ~cx & flipMaskX : cx);
		if (x >= RasterWidth)
			break;

		const auto colour = rowDefinition[cx];
		if (!allowTransparencies || (allowTransparencies && (colour > 0))) {
			const auto outputPixel = lineAddress + x;
			m_pixels[outputPixel] = m_colours->getColour(palette[colour]);
		}
	}
}