somewhat functional text rendering

src/ugui_font.c3

@@ -1,18 +1,217 @@
 module ugui;
 
 import schrift;
+import std::collections::map;
+import std::core::mem;
 
-struct Font @private {
+// unicode code point, different type for a different hash
+def Codepoint = uint;
+
+
+/* width and height of a glyph contain the kering advance
+ * (u,v)
+ *   +-------------*---+ -
+ *   |       ^     |   | ^
+ *   |       |oy   |   | |
+ *   |       v     |   | |
+ *   |      .ii.   |   | |
+ *   |     @@@@@@. |<->| |
+ *   |    V@Mio@@o |adv| |h
+ *   |    :i.  V@V |   | |
+ *   |      :oM@@M |   | |
+ *   |    :@@@MM@M |   | |
+ *   |    @@o  o@M |   | |
+ *   |<->:@@.  M@M |   | |
+ *   |ox  @@@o@@@@ |   | |
+ *   |    :M@@V:@@.|   | v
+ *   +-------------*---+ -
+ *   |<------------->|
+ *           w
+ */
+struct Glyph {
+	Codepoint code;
+	ushort u, v;
+	ushort w, h;
+	short adv, ox, oy;
+	short idx; // atlas index
+}
+
+const uint FONT_CACHED = 512;
+def GlyphTable = map::HashMap(<Codepoint, Glyph>) @private;
+
+fault UgFontError {
+	TTF_LOAD_FAILED,
+	MISSING_GLYPH,
+	BAD_GLYPH_METRICS,
+	RENDER_ERROR,
+}
+
+fault UgAtlasError {
+	CANNOT_PLACE,
+}
+
+// black and white atlas
+struct AtlasBW {
+	ushort width, height;
+	char[] buffer;
+
+	Point row;
+	ushort row_h;
+}
+
+struct Font {
 	schrift::Sft sft;
 	String path;
+	GlyphTable table;
+
+	float size;
+	float ascender, descender, linegap; // Line Metrics
+	AtlasBW[] atlas;
 }
 
-fn void! Ctx.font_load(&ctx, String path)
+fn void! AtlasBW.new(&atlas, ushort width, ushort height)
 {
-
+	atlas.width = width;
+	atlas.height = height;
+	atlas.buffer = mem::new_array(char, (usz)atlas.width*atlas.height);
 }
 
-fn void Ctx.font_free(&ctx)
+fn void AtlasBW.free(&atlas)
 {
-
+	free(atlas.buffer);
+}
+
+// place a rect inside the atlas
+// uses a row first algorithm
+// TODO: use a skyline algorithm https://jvernay.fr/en/blog/skyline-2d-packer/implementation/
+fn Point! AtlasBW.place(&atlas, char[] pixels, ushort w, ushort h)
+{
+	Point p;
+
+	if (atlas.row.x + w <= atlas.width && atlas.row.y + h <= atlas.height) {
+		p = atlas.row;
+	} else {
+		atlas.row.x = 0;
+		atlas.row.y = atlas.row.y + atlas.row_h;
+		atlas.row_h = 0;
+		if (atlas.row.x + w <= atlas.width && atlas.row.y + h <= atlas.height) {
+			p = atlas.row;
+		} else {
+			return UgAtlasError.CANNOT_PLACE?;
+		}
+	}
+
+	for (usz y = 0; y < h; y++) {
+		for (usz x = 0; x < w; x++) {
+			atlas.buffer[(usz)(p.y+y)*atlas.width + (p.x+x)] = pixels[y*w + x];
+		}
+	}
+
+	atlas.row.x += w;
+	if (h > atlas.row_h) {
+		atlas.row_h = h;
+	}
+
+	return p;
+}
+
+fn void! Font.load(&font, String path, uint height, float scale = 1)
+{
+	font.table.new_init(capacity: FONT_CACHED);
+	
+	font.size = height*scale;
+
+	font.sft = schrift::Sft{
+		.xScale = (double)font.size,
+		.yScale = (double)font.size,
+		.flags = schrift::SFT_DOWNWARD_Y,
+	};
+
+	font.sft.font = schrift::loadfile(path);
+	if (font.sft.font == null) {
+		return UgFontError.TTF_LOAD_FAILED?;
+	}
+
+	schrift::SftLMetrics lmetrics;
+	schrift::lmetrics(&font.sft, &lmetrics);
+	font.ascender  = (float)lmetrics.ascender;
+	font.descender = (float)lmetrics.descender;
+	font.linegap   = (float)lmetrics.lineGap;
+
+	// TODO: allocate buffer based on FONT_CACHED and the size of a sample letter
+	//       like the letter 'A'
+	font.atlas = mem::new_array(AtlasBW, 1);
+	ushort size = (ushort)font.size*512;
+	font.atlas[0].new(size, size)!;
+	
+	// preallocate the ASCII range
+//	for (char c = ' '; c < '~'; c++) {
+//		font.get_glyph((Codepoint)c)!;
+//	}
+}
+
+fn Glyph*! Font.get_glyph(&font, Codepoint code, bool* is_new = null)
+{
+	Glyph*! gp;
+	gp = font.table.get_ref(code);
+	
+	if (catch excuse = gp) {
+		if (excuse != SearchResult.MISSING) {
+			return excuse?;
+		}
+	} else {
+		if (is_new) { *is_new = false; }
+		return gp;
+	}
+
+	// missing glyph, render and place into an atlas
+	Glyph glyph;
+
+	schrift::SftGlyph gid;
+	schrift::SftGMetrics gmtx;
+	
+	if (schrift::lookup(&font.sft, code, &gid) < 0) {
+		return UgFontError.MISSING_GLYPH?;
+	}
+
+	if (schrift::gmetrics(&font.sft, gid, &gmtx) < 0) {
+		return UgFontError.BAD_GLYPH_METRICS?;
+	}
+
+	schrift::SftImage img = {
+		.width = gmtx.minWidth,
+		.height = gmtx.minHeight,
+	};
+	char[] pixels = mem::new_array(char, (usz)img.width * img.height);
+	img.pixels = pixels;
+	if (schrift::render(&font.sft, gid, img) < 0) {
+		return UgFontError.RENDER_ERROR?;
+	}
+
+	glyph.code = code;
+	glyph.w = (ushort)img.width;
+	glyph.h = (ushort)img.height;
+	glyph.ox = (short)-gmtx.leftSideBearing;
+	glyph.oy = (short)-gmtx.yOffset;
+	glyph.adv = (short)gmtx.advanceWidth;
+
+	Point uv = font.atlas[0].place(pixels, glyph.w, glyph.h)!;
+	glyph.idx = 0;
+	glyph.u = uv.x;
+	glyph.v = uv.y;
+
+	mem::free(pixels);
+
+	font.table.set(code, glyph);
+
+	if (is_new) { *is_new = true; }
+	return font.table.get_ref(code);
+}
+
+fn void Font.free(&font)
+{
+	foreach (atlas: font.atlas) {
+		atlas.free();
+	}
+	schrift::freefont(font.sft.font);
 }