ttf/ttf2.c

static u8
read_8(struct font_buffer *buf)
{
    u8 result = buf->data[buf->offset]; 
    buf->offset += 1;
    return(result);
}

static s8
read_8s(struct font_buffer *buf)
{
    s8 result = buf->data[buf->offset]; 
    buf->offset += 1;
    return(result);
}

static u16
be16(u8 *buf)
{
    u16 result = buf[0] << 8 | buf[1];
    return(result);
}

static s16
be16s(u8 *buf)
{
    s16 result = buf[0] << 8 | buf[1];
    return(result);
}

static u16
read_be16(struct font_buffer *buf)
{
    u16 result = be16(buf->data + buf->offset);
    buf->offset += 2;
    return(result);
}

static s16
read_be16s(struct font_buffer *buf)
{
    s16 result = be16s(buf->data + buf->offset);
    buf->offset += 2;
    return(result);
}

static u32
be32(u8 *buf)
{
    u32 result = ((u32) buf[0] << 24) | ((u32) buf[1] << 16) | ((u32) buf[2] << 8) | ((u32) buf[3]); 
    return(result);
}

static u32
read_be32(struct font_buffer *buf)
{
    u32 result = be32(buf->data + buf->offset);
    buf->offset += 4;
    return(result);
}

static f32
read_be214(struct font_buffer *buf)
{
    f32 result = read_be16s(buf) / 16384.0f;
    return(result);
}

static struct font_buffer
read_file(char *filename)
{
    FILE *file = fopen(filename, "rb");
    struct font_buffer result = { 0 };
    
    ASSERT(file);
    
    if (file) {
        fseek(file, 0, SEEK_END);
        result.size = ftell(file);
        result.data = malloc(result.size);
        fseek(file, 0, SEEK_SET);
        fread(result.data, result.size, 1, file);
        fclose(file);
    }
    
    return(result);
}

static u32
get_glyph_index_format12(struct ttf_font *font, u16 codepoint)
{
    u32 ngroups = be32(font->file.data + font->cmap_offset + 12);
    
    font->file.offset = font->cmap_offset + 16;
    
    // TODO: binsearch
    for (u32 g = 0; g < ngroups; ++g) {
        u32 start_charcode = read_be32(&font->file);
        u32 end_charcode = read_be32(&font->file);
        u32 start_glyphcode = read_be32(&font->file);
        
        if (start_charcode <= codepoint && codepoint <= end_charcode) {
            u32 glyph_index = start_glyphcode + (codepoint - start_charcode);
            return(glyph_index);
        }
        
        if (start_charcode > codepoint) {
            break;
        }
    }
    
    return(0);
}

static s16
get_glyph_index_format4(struct ttf_font *font, u16 codepoint)
{
    int segcount_x2 = be16(font->file.data + font->cmap_offset + 6);
    
    u16 *end_codes = (u16 *) (font->file.data + font->cmap_offset + 16);
    u16 *start_codes = (u16 *) (font->file.data + font->cmap_offset + 16 + segcount_x2 + 2);
    u16 *id_deltas = (u16 *) (font->file.data + font->cmap_offset + 16 + segcount_x2 * 2 + 2);
    u16 *id_range_offset = (u16 *) (font->file.data + font->cmap_offset + 16 + segcount_x2 * 3 + 2);
    
    int index = -1;
    
    for (int i = 0; i < segcount_x2 / 2; ++i) {
        u16 end_code = be16((u8 *) (end_codes + i));
		if (end_code >= codepoint) {
            index = i;
            break;
        }
	}
	
	if (index == -1) {
        return(0);
    }
    
    u16 start_code = be16((u8 *) (start_codes + index));
	if (start_code <= codepoint) {
        u16 ir_offset = be16((u8 *) (id_range_offset + index));
		if (ir_offset != 0) {
			u16 glyph_index = be16((u8 *) (id_range_offset 
                                           + index + ir_offset / 2 
                                           + (codepoint - start_code)));
            
			if (!glyph_index) {
                return(0);
            }
			
            u16 id_delta = be16((u8 *) (id_deltas + index));
            u16 result = (u16) (glyph_index + id_delta);
            
            return(result);
		}
        
        u16 id_delta = be16((u8 *) (id_deltas + index));
        u16 result = (u16) (codepoint + id_delta);
        
        return(result);
	}
    
	return(0);
}

static u16
get_glyph_index_format6(struct ttf_font *font, u16 codepoint)
{
    u16 first_code = be16(font->file.data + font->cmap_offset + 6);
    u16 entry_count = be16(font->file.data + font->cmap_offset + 8);
    u16 *glyph_index_array = (u16 *) (font->file.data + font->cmap_offset + 10);
    
    if (first_code <= codepoint && codepoint < first_code + entry_count) {
        u16 glyph_index = be16((u8 *) (glyph_index_array + (codepoint - first_code)));
        return(glyph_index);
    }
    
    return(0);
}

static u16
get_glyph_index_format0(struct ttf_font *font, u16 codepoint)
{
    u8 *glyph_index_array = font->file.data + font->cmap_offset + 6;
    
    if (codepoint <= 0xFF) {
        u8 glyph_index = glyph_index_array[codepoint];
        return(glyph_index);
    }
    
    return(0);
}

static u32
get_glyph_index(struct ttf_font *font, u16 codepoint) 
{
    u32 result = 0;
    
    switch (font->cmap_format) {
        case 0: {
            result = get_glyph_index_format0(font, codepoint);
            break;
        }
        
        case 12: {
            result = get_glyph_index_format12(font, codepoint);
            break;
        }
        
        case 6: {
            result = get_glyph_index_format6(font, codepoint);
            break;
        }
        
        case 4: {
            result = get_glyph_index_format4(font, codepoint);
            break;
        }
        
        default: {
            ASSERT(false);
        }
    }
    
    return(result);
}

static u32
get_glyph_offset(struct ttf_font *font, u32 glyph_index)
{
    u32 offset = 0;
    u32 offset_next;
    
    if (font->head.itl_format == 1) {
        font->file.offset = font->loca_offset + glyph_index * 4;
        offset = read_be32(&font->file);
        offset_next = read_be32(&font->file);
    } else {
        font->file.offset = font->loca_offset + glyph_index * 2;
        offset = read_be16(&font->file);
        offset *= 2;
        offset_next = read_be16(&font->file);
        offset_next *= 2;
    }
    
    if (offset == offset_next) {
        return(0);
    }
    
    return(offset);
}

static s16
get_current_coordinate(struct font_buffer *font_file, int flag_combined)
{
    s16 current_coordinate = 0;
    
    switch (flag_combined) {
        case 0: {
            current_coordinate = read_be16(font_file);
            break;
        }
        
        case 1: { 
            current_coordinate = 0; 
            break;
        }
        
        case 2: { 
            current_coordinate = read_8(font_file);
            current_coordinate *= -1;
            break;
        }
        
        case 3: { 
            current_coordinate = read_8(font_file);
            break;
        } 
    }
    
    return(current_coordinate);
}

static void
get_simple_glyph_points(struct font_buffer *font_file, u16 number_of_countours, struct glyph *result)
{
    u16 *end_pts_of_contours = calloc(1, number_of_countours * sizeof(u16));
    for (int c = 0; c < number_of_countours; ++c) {
        end_pts_of_contours[c] = read_be16(font_file);
    }
    
    // NOTE: skip instructions
    u16 instruction_length = read_be16(font_file);
    font_file->offset += instruction_length;
    
    int last_index = end_pts_of_contours[number_of_countours - 1];
    union glyph_flag *flags = calloc(1, last_index + 1);
    struct glyph_point *points = malloc((last_index + 2) * 2 * sizeof(struct v2));
    
    // NOTE: so that we can insert one point at the start if needed
    // points = points + 1;
    
    for (int i = 0; i < last_index + 1; ++i) {
        flags[i].flag = read_8(font_file);
        if (flags[i].repeat) {
            u8 repeat_count = read_8(font_file);
            while (repeat_count-- > 0) {
                i++;
                flags[i] = flags[i - 1];
            }
        }
    }
    
    s16 prev_coordinate = 0;
    int start = 0;
    int head = 0;
    
    for (int c = 0; c < number_of_countours; ++c) {
        int end = end_pts_of_contours[c];
        struct glyph_point first_point = { 0 };
        
        for (int i = start; i < end + 1; ++i) {
            // NOTE: read x coordinates
            int flag_combined = (flags[i].x_short << 1) | flags[i].x_short_pos;
            s16 current_coordinate = get_current_coordinate(font_file, flag_combined);
            s16 read_x = current_coordinate + prev_coordinate;
            
            int prev = i - 1;
            if (prev >= start) {
                //prev = end;
                
                if (!flags[i].on_curve && !flags[prev].on_curve) {
                    // NOTE: implicit on-curve point
                    points[head].on_curve = true;
                    points[head].x = (read_x + points[head - 1].x) / 2;
                    ++head;
                }
            }
            
            points[head].on_curve = flags[i].on_curve;
            points[head].x = read_x;
            ++head;
            
            if (i == start) {
                // NOTE: first iteration could not have inserted an implicit point
                first_point = points[head - 1];
            }
            
            prev_coordinate = read_x;
        }
        
        if (!flags[start].on_curve && !flags[end].on_curve) {
            points[head].on_curve = true;
            points[head].x = (first_point.x + points[head - 1].x) / 2;
            ++head;
        }
        
        start = end + 1;
    }
    
    
    prev_coordinate = 0;
    start = 0;
    head = 0;
    
    int added_points = 0;
    
    for (int c = 0; c < number_of_countours; ++c) {
        int end = end_pts_of_contours[c];
        struct glyph_point first_point = { 0 };
        
        for (int i = start; i < end + 1; ++i) {
            // NOTE: read y coordinates
            int flag_combined = (flags[i].y_short << 1) | flags[i].y_short_pos;
            s16 current_coordinate = get_current_coordinate(font_file, flag_combined);
            s16 read_y = current_coordinate + prev_coordinate;
            
            int prev = i - 1;
            if (prev >= start) {
                //prev = end;
                
                if (!flags[i].on_curve && !flags[prev].on_curve) {
                    // NOTE: implicit on-curve point
                    points[head].on_curve = true;
                    points[head].y = (read_y + points[head - 1].y) / 2;
                    ++head;
                    ++added_points;
                }
            }
            
            points[head].on_curve = flags[i].on_curve;
            points[head].y = read_y;
            ++head;
            
            prev_coordinate = read_y;
            
            if (i == start) {
                // NOTE: first iteration could not have inserted an implicit point
                first_point = points[head - 1];
            }
        }
        
        if (!flags[start].on_curve && !flags[end].on_curve) {
            points[head].on_curve = true;
            points[head].y = (first_point.y + points[head - 1].y) / 2;
            ++head;
            ++added_points;
        }
        
        start = end + 1;
        end_pts_of_contours[c] += added_points;
    }
    
    
    result->points = points;
    result->ncontours = number_of_countours;
    result->end_pts_of_contours = end_pts_of_contours;
}

static struct glyph
get_glyph_outline(struct ttf_font *font, u32 glyph_index)
{
    u32 glyph_offset = get_glyph_offset(font, glyph_index);
    struct font_buffer *font_file = &font->file;
    
    font_file->offset = font->glyf_offset + glyph_offset;
    
    struct glyph result = { 0 };
    s16 number_of_countours = read_be16(font_file);
    
    result.xmin = read_be16(font_file);
    result.ymin = read_be16(font_file);
    result.xmax = read_be16(font_file);
    result.ymax = read_be16(font_file);
    
    if (number_of_countours > 0) {
        // NOTE: simple glyph
        get_simple_glyph_points(font_file, number_of_countours, &result);
    } else if (number_of_countours < 0) {
        // NOTE: compund glyph
        int head = 0;
        
        result.end_pts_of_contours = malloc(font->maxp.max_component_contours * sizeof(u16));
        result.points = malloc(font->maxp.max_component_points * 2 * sizeof(struct glyph_point));
        
        for (;;) {
            u16 flags = read_be16(font_file);
            u16 component_index = read_be16(font_file);
            
            f32 matrix[6] = {1, 0, 0, 1, 0, 0}; /* NOTE(aolo2): matrix stuff is highjacked from stb */
            
            if (flags & ARG_1_AND_2_ARE_WORDS) {
                matrix[4] = read_be16(font_file);
                matrix[5] = read_be16(font_file);
            } else {
                matrix[4] = read_8s(font_file);
                matrix[5] = read_8s(font_file);
            }
            
            if (flags & WE_HAVE_A_SCALE) {
                f32 scale = read_be214(font_file);
                matrix[0] = scale;
                matrix[1] = 0;
                matrix[2] = 0;
                matrix[3] = scale;
            } else if (flags & WE_HAVE_AN_X_AND_Y_SCALE ) {
                f32 xscale = read_be214(font_file);
                f32 yscale = read_be214(font_file);
                matrix[0] = xscale;
                matrix[1] = 0;
                matrix[2] = 0;
                matrix[3] = yscale;
            } else if (flags & WE_HAVE_A_TWO_BY_TWO) {
                f32 xscale = read_be214(font_file);
                f32 scale01 = read_be214(font_file);
                f32 scale10 = read_be214(font_file);
                f32 yscale = read_be214(font_file);
                matrix[0] = xscale;
                matrix[1] = scale01;
                matrix[2] = scale10;
                matrix[3] = yscale;
            }
            
            f32 m = sqrtf(matrix[0] * matrix[0] + matrix[1] * matrix[1]);
            f32 n = sqrtf(matrix[2] * matrix[2] + matrix[3] * matrix[3]);
            
            u32 saved_offset = font_file->offset;
            struct glyph component = get_glyph_outline(font, component_index);
            font_file->offset = saved_offset;
            
            int startv = 0;
            for (int c = 0; c < component.ncontours; ++c) {
                int endv = component.end_pts_of_contours[c] + 1;
                
                for (int v = startv; v < endv; ++v) {
                    s16 x = component.points[v].x;
                    s16 y = component.points[v].y;
                    
                    result.points[head].x = m * (matrix[0] * x + matrix[2] * y + matrix[4]);
                    result.points[head].y = n * (matrix[1] * x + matrix[3] * y + matrix[5]);
                    result.points[head].on_curve = component.points[v].on_curve;
                    ++head;
                }
                
                startv = endv;
                result.end_pts_of_contours[result.ncontours] = head - 1;
                ++result.ncontours;
            }
            
            if (!(flags & MORE_COMPONENTS)) {
                break;
            }
        }
    } else {
        // NOTE: space
        //advance = 0; // TODO
    }
    
    return(result);
}

static void
get_hmtx(struct ttf_font *font, u32 glyph_index, struct glyph *dest)
{
    struct font_buffer font_file = font->file;
    
    // TODO: monospaced font only has one record
    
    font_file.offset = font->hmtx_offset + glyph_index * 4;
    
    dest->advance = read_be16(&font_file);
    dest->lsb = read_be16s(&font_file);
}

static struct glyph
get_outline(struct ttf_font *font, u16 codepoint)
{
    u32 glyph_index = get_glyph_index(font, codepoint);
    
    struct glyph result = get_glyph_outline(font, glyph_index);
    get_hmtx(font, glyph_index, &result);
    
#if 1
    int ymax = result.ymax;
    //int ymin = result.ymin;
    
    for (int p = 0; p < result.end_pts_of_contours[result.ncontours - 1] + 1; ++p) {
        struct glyph_point *gp = result.points + p;
        gp->y = ymax - gp->y;
        //gp->y += ymin;
    }
#endif 
    
    return(result);
}

static u16
read_offset_table(struct font_buffer *file)
{
    u16 num_tables = be16(file->data + 4);
    return(num_tables);
}

static struct font_directory
read_font_directory(struct font_buffer *file)
{
    struct font_directory result = { 0 };
    u16 table_count = read_offset_table(file);
    
    for (int i = 0; i < table_count; ++i) {
        u32 tag = be32(file->data + 12 + 16 * i + 0);
        u32 offset = be32(file->data + 12 + 16 * i + 8);
        
        switch (tag) {
            case 0x636d6170: {
                /* cmap */
                result.cmap_offset = offset;
                break;
            }
            
            case 0x6c6f6361: {
                /* loca */
                result.loca_offset = offset;
                break;
            }
            
            case 0x68656164: {
                /* head */
                result.head_offset = offset;
                break;
            }
            
            case 0x676c7966: {
                /* glyf */
                result.glyf_offset = offset;
                break;
            }
            
            case 0x686d7478: {
                /* hmtx */
                result.hmtx_offset = offset;
                break;
            }
            
            case 0x6d617870: {
                /* maxp */
                result.maxp_offset = offset;
                break;
            }
            
            case 0x68686561: {
                /* hhea */
                result.hhea_offset = offset;
                break;
            }
        }
    }
    
    return(result);
}

static void
read_head(struct font_directory font_dir, struct ttf_font *font)
{
    font->head.units_per_em = be16(font->file.data + font_dir.head_offset + 18);
    font->head.itl_format = be16(font->file.data + font_dir.head_offset + 50);
}

static void
read_hhea(struct font_directory font_dir, struct ttf_font *font)
{
    font->hhea.ascent = be16s(font->file.data + font_dir.hhea_offset + 4);
    font->hhea.descent = be16s(font->file.data + font_dir.hhea_offset + 6);
    font->hhea.line_gap = be16s(font->file.data + font_dir.hhea_offset + 10);
    font->hhea.max_advance = be16(font->file.data + font_dir.hhea_offset + 14);
}

static void
read_cmap(struct font_directory font_dir, struct ttf_font *font)
{
    font->file.offset = font_dir.cmap_offset + 2;
    
    u16 num_tables = read_be16(&font->file);
    
    for (int st = 0; st < num_tables; ++st) {
        u16 platform_id = read_be16(&font->file);
        u16 platform_specific_id = read_be16(&font->file);
        u32 subtable_offset = read_be32(&font->file);
        
        if ((platform_id == 0 && (platform_specific_id == 3 || platform_specific_id == 4)) ||
            (platform_id == 3 && ((platform_specific_id == 1 || platform_specific_id == 10))))
        {
            font->cmap_format = be16(font->file.data + font_dir.cmap_offset + subtable_offset);
            font->cmap_offset = font_dir.cmap_offset + subtable_offset;
        }
    }
}

static void
read_maxp(struct font_directory font_dir, struct ttf_font *font)
{
    font->maxp.max_component_points = be16(font->file.data + font_dir.maxp_offset + 10);
    font->maxp.max_component_contours = be16(font->file.data + font_dir.maxp_offset + 12);
}

static struct ttf_font
parse_ttf_file(char *filename, char *fontname)
{
    struct ttf_font result = { 0 };
    struct font_buffer font_file = read_file(filename);
    struct font_directory font_dir = read_font_directory(&font_file);
    
    result.file = font_file;
    result.glyf_offset = font_dir.glyf_offset;
    result.loca_offset = font_dir.loca_offset;
    result.hmtx_offset = font_dir.hmtx_offset;
    
    read_head(font_dir, &result);
    read_maxp(font_dir, &result);
    read_cmap(font_dir, &result);
    read_hhea(font_dir, &result);
    
    result.name = fontname;
    
    return(result);
}