计算FreeType字形渲染的位置?

时间:2018-11-12 18:17:08

标签: c++ opengl true-type-fonts freetype

我正在尝试使用FreeType和OpenGL渲染一些文本:

example image

text = "fghjRT-123VWYUGHJ$@%"

有两个问题:

  1. 为什么字母之间有这么奇怪的空格? (预付款有什么问题?)
  2. 如何计算最高位置(或原点位置)? (黄色边框和字符之间有一些空格。我想将其附加到顶部边框)

我的渲染代码:

/* top left position on screen to render text (yellow border) */
Vector<2> pos = params.rect.left_top();

/* adjust to bottom (how to get correct origin position?) */
pos.y() += font->char_size();

for (char ch : params.text)
{
    /* contains info after freetype FT_LoadGlyph */
    FontChar const* char_info = font->find_char(ch);

    RectF char_rect(
        pos - char_info->bearing(), /* left, top */
        char_info->glyph_rect().size() /* width, height */
    );

    /* convert screen coordinates to OpenGL coordinates */
    RectF dr = calc_coord(m_screen_size, char_rect);

    /* pack position of glyph and it's texture from bitmap
     * into one sequence of data
     */
    Vector<16> spr_coords = pack_spr_info(dr, char_info->rect());

    m_sprite_buffer.push_back(spr_coords);

    /* move pen by advance */
    pos.x() += char_info->advance();
}

我的字形加载代码片段:

FT_GlyphSlot slot = face->glyph;

char_info->bearing() = {
    slot->metrics.horiBearingX / 64.0f,
    slot->metrics.horiBearingY / 64.0f
};

char_info->glyph_rect() = { 
    slot->metrics.horiBearingX / 64.0f, /* left */
    slot->metrics.horiBearingY / 64.0f, /* top */
    slot->metrics.width / 64.0f, /* width */
    slot->metrics.height / 64.0f /* height */
};

char_info->advance() = slot->metrics.horiAdvance / 64.0f;

1 个答案:

答案 0 :(得分:2)

好,我自己找到答案了。
我的char_rect职位计算有误。正确方法:

RectF char_rect(
    pos.x() + char_info->bearing().x(), /* left */
    pos.y() - char_info->bearing().y(), /* top */
    char_info->glyph_rect().size() /* width, height */
);

从顶部边框调整查找基线(原点)的方式:

Vector<2> pos = params.rect.left_top();
pos.y() += font->ascend(); /* move pen down on the screen */

位置:

FT_Face face = ...;
font->ascend() = face->ascender / 32;