godot/tools/editor/io_plugins/editor_atlas.cpp

/*************************************************************************/
/*  editor_atlas.cpp                                                     */
/*************************************************************************/
/*                       This file is part of:                           */
/*                           GODOT ENGINE                                */
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/* Copyright (c) 2007-2015 Juan Linietsky, Ariel Manzur.                 */
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#include "editor_atlas.h"


struct _EditorAtlasWorkRect {

	Size2i s;
	Point2i p;
	int idx;
	_FORCE_INLINE_ bool operator<(const _EditorAtlasWorkRect& p_r) const { return s.width > p_r.s.width; };
};

struct _EditorAtlasWorkRectResult {

	Vector<_EditorAtlasWorkRect> result;
	int max_w;
	int max_h;
};

void EditorAtlas::fit(const Vector<Size2i>& p_rects,Vector<Point2i>& r_result, Size2i& r_size) {

	//super simple, almost brute force scanline stacking fitter
	//it's pretty basic for now, but it tries to make sure that the aspect ratio of the
	//resulting atlas is somehow square. This is necesary because video cards have limits
	//on texture size (usually 2048 or 4096), so the more square a texture, the more chances
	//it will work in every hardware.
	// for example, it will prioritize a 1024x1024 atlas (works everywhere) instead of a
	// 256x8192 atlas (won't work anywhere).

	ERR_FAIL_COND(p_rects.size()==0);

	Vector<_EditorAtlasWorkRect> wrects;
	wrects.resize(p_rects.size());
	for(int i=0;i<p_rects.size();i++) {
		wrects[i].s=p_rects[i];
		wrects[i].idx=i;
	}
	wrects.sort();
	int widest = wrects[0].s.width;

	Vector<_EditorAtlasWorkRectResult> results;

	for(int i=0;i<=12;i++) {

		int w = 1<<i;
		int max_h=0;
		int max_w=0;
		if ( w < widest )
			continue;

		Vector<int> hmax;
		hmax.resize(w);
		for(int j=0;j<w;j++)
			hmax[j]=0;

		//place them
		int ofs=0;
		int limit_h=0;
		for(int j=0;j<wrects.size();j++) {


			if (ofs+wrects[j].s.width > w) {

				ofs=0;
			}

			int from_y=0;
			for(int k=0;k<wrects[j].s.width;k++) {

				if (hmax[ofs+k] > from_y)
					from_y=hmax[ofs+k];
			}

			wrects[j].p.x=ofs;
			wrects[j].p.y=from_y;
			int end_h = from_y+wrects[j].s.height;
			int end_w = ofs+wrects[j].s.width;
			if (ofs==0)
				limit_h=end_h;

			for(int k=0;k<wrects[j].s.width;k++) {

				hmax[ofs+k]=end_h;
			}

			if (end_h > max_h)
				max_h=end_h;

			if (end_w > max_w)
				max_w=end_w;

			if (ofs==0 || end_h>limit_h ) //while h limit not reched, keep stacking
				ofs+=wrects[j].s.width;

		}

		_EditorAtlasWorkRectResult result;
		result.result=wrects;
		result.max_h=max_h;
		result.max_w=max_w;
		results.push_back(result);

	}

	//find the result with the best aspect ratio

	int best=-1;
	float best_aspect=1e20;

	for(int i=0;i<results.size();i++) {

		float h = nearest_power_of_2(results[i].max_h);
		float w = nearest_power_of_2(results[i].max_w);
		float aspect = h>w ? h/w : w/h;
		if (aspect < best_aspect) {
			best=i;
			best_aspect=aspect;
		}
	}

	r_result.resize(p_rects.size());

	for(int i=0;i<p_rects.size();i++) {

		r_result[ results[best].result[i].idx ]=results[best].result[i].p;
	}

	r_size=Size2(results[best].max_w,results[best].max_h );

}