devilutionX/Source/engine/render/common_impl.h

/**
 * @file common_impl.h
 *
 * Common code for implementing various renderers.
 */
#pragma once

#include <cstddef>
#include <cstdint>

#include "engine.h"
#include "engine/point.hpp"
#include "engine/render/blit_impl.hpp"
#include "lighting.h"
#include "utils/attributes.h"

namespace devilution {

struct ClipX {
	int_fast16_t left;
	int_fast16_t right;
	int_fast16_t width;
};

DVL_ALWAYS_INLINE DVL_ATTRIBUTE_HOT ClipX CalculateClipX(int_fast16_t x, std::size_t w, const Surface &out)
{
	ClipX clip;
	clip.left = static_cast<int_fast16_t>(x < 0 ? -x : 0);
	clip.right = static_cast<int_fast16_t>(static_cast<int_fast16_t>(x + w) > out.w() ? x + w - out.w() : 0);
	clip.width = static_cast<int_fast16_t>(w - clip.left - clip.right);
	return clip;
}

// Source data for rendering backwards: first line of input -> last line of output.
struct RenderSrcBackwards {
	const uint8_t *begin;
	const uint8_t *end;
	uint_fast16_t width;
};

// Source data for rendering forwards: first line of input -> first line of output.
struct RenderSrcForwards {
	const uint8_t *begin;
	uint_fast16_t width;
	uint_fast16_t height;
};

struct SkipSize {
	int_fast16_t wholeLines;
	int_fast16_t xOffset;
};
DVL_ALWAYS_INLINE DVL_ATTRIBUTE_HOT SkipSize GetSkipSize(int_fast16_t overrun, int_fast16_t srcWidth)
{
	SkipSize result;
	result.wholeLines = overrun / srcWidth;
	result.xOffset = overrun - srcWidth * result.wholeLines;
	return result;
}

using GetBlitCommandFn = BlitCommand (*)(const uint8_t *src);

template <GetBlitCommandFn GetBlitCommand>
DVL_ALWAYS_INLINE DVL_ATTRIBUTE_HOT const uint8_t *SkipRestOfLine(const uint8_t *src, unsigned remainingWidth)
{
	while (remainingWidth > 0) {
		const BlitCommand cmd = GetBlitCommand(src);
		src = cmd.srcEnd;
		remainingWidth -= cmd.length;
	}
	return src;
}

template <GetBlitCommandFn GetBlitCommand>
DVL_ALWAYS_INLINE DVL_ATTRIBUTE_HOT const uint8_t *SkipRestOfLineWithOverrun(
    const uint8_t *src, int_fast16_t srcWidth, SkipSize &skipSize)
{
	int_fast16_t remainingWidth = srcWidth - skipSize.xOffset;
	while (remainingWidth > 0) {
		const BlitCommand cmd = GetBlitCommand(src);
		src = cmd.srcEnd;
		remainingWidth -= cmd.length;
	}
	if (remainingWidth < 0) {
		skipSize = GetSkipSize(-remainingWidth, srcWidth);
		++skipSize.wholeLines;
	} else {
		skipSize.wholeLines = 1;
		skipSize.xOffset = 0;
	}
	return src;
}

template <GetBlitCommandFn GetBlitCommand>
DVL_ALWAYS_INLINE DVL_ATTRIBUTE_HOT void SkipLinesForRenderBackwards(
    Point &position, RenderSrcBackwards &src, int_fast16_t dstHeight)
{
	while (position.y >= dstHeight && src.begin != src.end) {
		src.begin = SkipRestOfLine<GetBlitCommand>(src.begin, src.width);
		--position.y;
	}
}

// Returns the horizontal overrun.
template <GetBlitCommandFn GetBlitCommand>
DVL_ALWAYS_INLINE DVL_ATTRIBUTE_HOT int_fast16_t SkipLinesForRenderBackwardsWithOverrun(
    Point &position, RenderSrcBackwards &src, int_fast16_t dstHeight)
{
	SkipSize skipSize = { 0, 0 };
	while (position.y >= dstHeight && src.begin != src.end) {
		src.begin = SkipRestOfLineWithOverrun<GetBlitCommand>(
		    src.begin, static_cast<int_fast16_t>(src.width), skipSize);
		position.y -= static_cast<int>(skipSize.wholeLines);
	}
	return skipSize.xOffset;
}

template <GetBlitCommandFn GetBlitCommand>
DVL_ALWAYS_INLINE DVL_ATTRIBUTE_HOT void SkipLinesForRenderForwards(Point &position, RenderSrcForwards &src, unsigned lineEndPadding)
{
	while (position.y < 0 && src.height != 0) {
		src.begin = SkipRestOfLine<GetBlitCommand>(src.begin, src.width) + lineEndPadding;
		++position.y;
		--src.height;
	}
}

template <
    bool TransparentCommandCanCrossLines,
    GetBlitCommandFn GetBlitCommand,
    typename BlitFn>
void DoRenderBackwardsClipY(
    const Surface &out, Point position, RenderSrcBackwards src, BlitFn &&blitFn)
{
	// Skip the bottom clipped lines.
	int_fast16_t xOffset;
	if (TransparentCommandCanCrossLines) {
		xOffset = SkipLinesForRenderBackwardsWithOverrun<GetBlitCommand>(position, src, out.h());
	} else {
		SkipLinesForRenderBackwards<GetBlitCommand>(position, src, out.h());
	}
	if (src.begin >= src.end)
		return;

	auto *dst = &out[position];
	const auto *dstBegin = out.begin();
	const int dstPitch = out.pitch();
	while (src.begin != src.end && dst >= dstBegin) {
		auto remainingWidth = static_cast<int_fast16_t>(src.width);
		if (TransparentCommandCanCrossLines) {
			remainingWidth -= xOffset;
			dst += xOffset;
		}
		while (remainingWidth > 0) {
			BlitCommand cmd = GetBlitCommand(src.begin);
			blitFn(cmd, dst, src.begin + 1);
			src.begin = cmd.srcEnd;
			dst += cmd.length;
			remainingWidth -= cmd.length;
		}
		dst -= dstPitch + src.width - remainingWidth;

		if (TransparentCommandCanCrossLines) {
			if (remainingWidth < 0) {
				const auto skipSize = GetSkipSize(-remainingWidth, static_cast<int_fast16_t>(src.width));
				xOffset = skipSize.xOffset;
				dst -= skipSize.wholeLines * dstPitch;
			} else {
				xOffset = 0;
			}
		}
	}
}

template <
    bool TransparentCommandCanCrossLines,
    GetBlitCommandFn GetBlitCommand,
    typename BlitFn>
void DoRenderBackwardsClipXY(
    const Surface &out, Point position, RenderSrcBackwards src, ClipX clipX, BlitFn &&blitFn)
{
	// Skip the bottom clipped lines.
	int_fast16_t xOffset;
	if (TransparentCommandCanCrossLines) {
		xOffset = SkipLinesForRenderBackwardsWithOverrun<GetBlitCommand>(position, src, out.h());
	} else {
		SkipLinesForRenderBackwards<GetBlitCommand>(position, src, out.h());
	}
	if (src.begin >= src.end)
		return;

	position.x += static_cast<int>(clipX.left);
	auto *dst = &out[position];
	const auto *dstBegin = out.begin();
	const int dstPitch = out.pitch();

	while (src.begin != src.end && dst >= dstBegin) {
		// Skip initial src if clipping on the left.
		// Handles overshoot, i.e. when the RLE segment goes into the unclipped area.
		int_fast16_t remainingWidth = clipX.width;
		int_fast16_t remainingLeftClip = clipX.left;
		if (TransparentCommandCanCrossLines) {
			remainingLeftClip -= xOffset;
			if (remainingLeftClip < 0) {
				dst += std::min<unsigned>(remainingWidth, -remainingLeftClip);
				remainingWidth += remainingLeftClip;
			}
		}
		while (remainingLeftClip > 0) {
			BlitCommand cmd = GetBlitCommand(src.begin);
			if (static_cast<int_fast16_t>(cmd.length) > remainingLeftClip) {
				const auto overshoot = static_cast<int>(cmd.length - remainingLeftClip);
				cmd.length = std::min<unsigned>(remainingWidth, overshoot);
				blitFn(cmd, dst, src.begin + 1 + remainingLeftClip);
				dst += cmd.length;
				remainingWidth -= overshoot;
				src.begin = cmd.srcEnd;
				break;
			}
			src.begin = cmd.srcEnd;
			remainingLeftClip -= cmd.length;
		}
		while (remainingWidth > 0) {
			BlitCommand cmd = GetBlitCommand(src.begin);
			const unsigned unclippedLength = cmd.length;
			cmd.length = std::min<unsigned>(remainingWidth, cmd.length);
			blitFn(cmd, dst, src.begin + 1);
			src.begin = cmd.srcEnd;
			dst += cmd.length;
			remainingWidth -= unclippedLength; // result can be negative
		}

		// We've advanced `dst` by `clipX.width`.
		//
		// Set dst to (position.y - 1, position.x)
		dst -= dstPitch + clipX.width;

		if (TransparentCommandCanCrossLines) {
			// `remainingWidth` can be negative, in which case it is the amount of pixels
			// that the source has overran the line.
			remainingWidth += clipX.right;
			SkipSize skipSize { 0, 0 };
			if (remainingWidth > 0) {
				skipSize.xOffset = static_cast<int_fast16_t>(src.width) - remainingWidth;
				src.begin = SkipRestOfLineWithOverrun<GetBlitCommand>(
				    src.begin, static_cast<int_fast16_t>(src.width), skipSize);
				--skipSize.wholeLines;
			} else if (remainingWidth < 0) {
				skipSize = GetSkipSize(-remainingWidth, static_cast<int_fast16_t>(src.width));
			}
			xOffset = skipSize.xOffset;
			dst -= dstPitch * skipSize.wholeLines;
		} else {
			src.begin = SkipRestOfLine<GetBlitCommand>(src.begin, clipX.right + remainingWidth);
		}
	}
}

template <
    bool TransparentCommandCanCrossLines,
    GetBlitCommandFn GetBlitCommand,
    typename BlitFn>
void DoRenderBackwards(
    const Surface &out, Point position, const uint8_t *src, size_t srcSize, unsigned srcWidth,
    BlitFn &&blitFn)
{
	const ClipX clipX = CalculateClipX(position.x, srcWidth, out);
	if (clipX.width <= 0)
		return;
	RenderSrcBackwards srcForBackwards { src, src + srcSize, static_cast<uint_fast16_t>(srcWidth) };
	if (static_cast<std::size_t>(clipX.width) == srcWidth) {
		DoRenderBackwardsClipY<TransparentCommandCanCrossLines, GetBlitCommand>(
		    out, position, srcForBackwards, std::forward<BlitFn>(blitFn));
	} else {
		DoRenderBackwardsClipXY<TransparentCommandCanCrossLines, GetBlitCommand>(
		    out, position, srcForBackwards, clipX, std::forward<BlitFn>(blitFn));
	}
}

template <
    GetBlitCommandFn GetBlitCommand,
    typename BlitFn,
    typename TransformBlitCommandFn>
void DoRenderForwardsClipY(
    const Surface &out, Point position, RenderSrcForwards src,
    BlitFn &&blitFn, TransformBlitCommandFn &&transformBlitCommandFn)
{
	// Even padding byte is specific to PCX which is the only renderer that uses this function currently.
	const unsigned srcLineEndPadding = src.width % 2;
	SkipLinesForRenderForwards<GetBlitCommand>(position, src, srcLineEndPadding);
	src.height = static_cast<uint_fast16_t>(std::min<int_fast16_t>(out.h() - position.y, src.height));

	const auto dstSkip = static_cast<unsigned>(out.pitch());
	uint8_t *dst = &out[position];
	for (unsigned y = 0; y < src.height; y++) {
		for (unsigned x = 0; x < src.width;) {
			BlitCommand cmd = GetBlitCommand(src.begin);
			cmd = transformBlitCommandFn(cmd);
			blitFn(cmd, dst + x, src.begin + 1);
			src.begin = cmd.srcEnd;
			x += cmd.length;
		}
		src.begin += srcLineEndPadding;
		dst += dstSkip;
	}
}

template <
    GetBlitCommandFn GetBlitCommand,
    typename BlitFn,
    typename TransformBlitCommandFn>
void DoRenderForwardsClipXY(
    const Surface &out, Point position, RenderSrcForwards src, ClipX clipX,
    BlitFn &&blitFn, TransformBlitCommandFn &&transformBlitCommandFn)
{
	const unsigned srcLineEndPadding = src.width % 2;
	SkipLinesForRenderForwards<GetBlitCommand>(position, src, srcLineEndPadding);
	src.height = static_cast<uint_fast16_t>(std::min<int_fast16_t>(out.h() - position.y, src.height));

	position.x += static_cast<int>(clipX.left);
	const auto dstSkip = static_cast<unsigned>(out.pitch() - clipX.width);
	uint8_t *dst = &out[position];
	for (unsigned y = 0; y < src.height; y++) {
		// Skip initial src if clipping on the left.
		// Handles overshoot, i.e. when the RLE segment goes into the unclipped area.
		int_fast16_t remainingWidth = clipX.width;
		auto remainingLeftClip = clipX.left;
		while (remainingLeftClip > 0) {
			BlitCommand cmd = GetBlitCommand(src.begin);
			if (static_cast<int_fast16_t>(cmd.length) > remainingLeftClip) {
				const uint_fast16_t overshoot = cmd.length - remainingLeftClip;
				cmd.length = std::min<unsigned>(overshoot, remainingWidth);
				cmd = transformBlitCommandFn(cmd);
				blitFn(cmd, dst, src.begin + 1 + remainingLeftClip);
				src.begin = cmd.srcEnd;
				dst += cmd.length;
				remainingWidth -= static_cast<int_fast16_t>(overshoot);
				break;
			}
			src.begin = cmd.srcEnd;
			remainingLeftClip -= cmd.length;
		}
		while (remainingWidth > 0) {
			BlitCommand cmd = GetBlitCommand(src.begin);
			const unsigned unclippedLength = cmd.length;
			cmd = transformBlitCommandFn(cmd);
			cmd.length = std::min<unsigned>(cmd.length, remainingWidth);
			blitFn(cmd, dst, src.begin + 1);
			src.begin = cmd.srcEnd;
			dst += cmd.length;
			remainingWidth -= unclippedLength; // result can be negative
		}
		src.begin = SkipRestOfLine<GetBlitCommand>(src.begin, clipX.right + remainingWidth) + srcLineEndPadding;
		dst += dstSkip;
	}
}

template <
    GetBlitCommandFn GetBlitCommand,
    typename BlitFn,
    typename TransformBlitCommandFn>
void DoRenderForwards(
    const Surface &out, Point position, const uint8_t *src, unsigned srcWidth, unsigned srcHeight,
    BlitFn &&blitFn, TransformBlitCommandFn &&transformBlitCommandFn)
{
	if (position.y >= out.h() || position.y + srcHeight <= 0)
		return;
	const ClipX clipX = CalculateClipX(position.x, srcWidth, out);
	if (clipX.width <= 0)
		return;
	RenderSrcForwards srcForForwards { src, static_cast<uint_fast16_t>(srcWidth), static_cast<uint_fast16_t>(srcHeight) };
	if (static_cast<unsigned>(clipX.width) == srcWidth) {
		DoRenderForwardsClipY<GetBlitCommand>(
		    out, position, srcForForwards, std::forward<BlitFn>(blitFn), std::forward<TransformBlitCommandFn>(transformBlitCommandFn));
	} else {
		DoRenderForwardsClipXY<GetBlitCommand>(
		    out, position, srcForForwards, clipX, std::forward<BlitFn>(blitFn), std::forward<TransformBlitCommandFn>(transformBlitCommandFn));
	}
}

template <bool North, bool West, bool South, bool East>
DVL_ALWAYS_INLINE DVL_ATTRIBUTE_HOT void RenderOutlineForPixel(uint8_t *dst, int dstPitch, uint8_t color)
{
	if (North)
		dst[-dstPitch] = color;
	if (West)
		dst[-1] = color;
	if (East)
		dst[1] = color;
	if (South)
		dst[dstPitch] = color;
}

template <bool North, bool West, bool South, bool East, bool SkipColorIndexZero = true>
DVL_ALWAYS_INLINE DVL_ATTRIBUTE_HOT void RenderOutlineForPixel(uint8_t *dst, int dstPitch, uint8_t srcColor, uint8_t color)
{
	if (SkipColorIndexZero && srcColor == 0)
		return;
	RenderOutlineForPixel<North, West, South, East>(dst, dstPitch, color);
}

template <bool North, bool West, bool South, bool East>
DVL_ALWAYS_INLINE DVL_ATTRIBUTE_HOT void RenderOutlineForPixels(uint8_t *dst, int dstPitch, int width, uint8_t color)
{
	if (North)
		std::memset(dst - dstPitch, color, width);

	if (West && East)
		std::memset(dst - 1, color, width + 2);
	else if (West)
		std::memset(dst - 1, color, width);
	else if (East)
		std::memset(dst + 1, color, width);

	if (South)
		std::memset(dst + dstPitch, color, width);
}

template <bool North, bool West, bool South, bool East, bool SkipColorIndexZero = true>
DVL_ALWAYS_INLINE DVL_ATTRIBUTE_HOT void RenderOutlineForPixels(uint8_t *dst, int dstPitch, int width, const uint8_t *src, uint8_t color)
{
	if (SkipColorIndexZero) {
		while (width-- > 0)
			RenderOutlineForPixel<North, West, South, East>(dst++, dstPitch, *src++, color);
	} else {
		RenderOutlineForPixels<North, West, South, East>(dst, dstPitch, width, color);
	}
}

} // namespace devilution