ft_render.cpp
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// This file is part of OpenCV project.
// It is subject to the license terms in the LICENSE file found in the top-level directory
// of this distribution and at http://opencv.org/license.html.
//
// Copyright (C) 2019 Intel Corporation
#include "precomp.hpp"
#include "ft_render.hpp"
#ifdef HAVE_FREETYPE
#include "ft_render_priv.hpp"
#include <opencv2/gapi/util/throw.hpp>
#include <opencv2/gapi/own/assert.hpp>
cv::gapi::wip::draw::FTTextRender::Priv::Priv(const std::string& path)
{
if (FT_Init_FreeType(&m_library) != 0)
{
cv::util::throw_error(std::runtime_error("Failed to initialize FT"));
}
if (FT_New_Face(m_library, path.c_str(), 0, &m_face))
{
FT_Done_FreeType(m_library);
cv::util::throw_error(std::runtime_error("Failed to create a font face"));
}
}
cv::Size cv::gapi::wip::draw::FTTextRender::Priv::getTextSize(const std::wstring& text, int fh, int* baseline)
{
//
//
//
// ^ diff between size and advance(2)
// | ______________ width width |<->|
// | | ** | |<------>| <------------|--->
// | | * * | |________| |____________|___|________
// | left | * * | left |* * * * | | * * * * *| | ^ ^
// |<---->| ** ** ** | <----->|* *| | * | | t | |
// | | * * | | |* *| | * | | o | h |
// | | * * | | |* * * * | | * (1) | p | e | baseline
// O------|*------------*|-----O----- |*-------|-|----O--*----O---|-----*-i-|------------>
// | |______________| | |* | |* | * | | ^ g |
// | | | | |* | |* | * | | b | h |
// | | width | | |* | |* | * | | o | t |
// | |<------------>| | |* | | * *|* | | t | |
// | | |________| |____|_______|___|_____|___*
// | advance | advance | |advance| (advance maybe less than width)
// <---------------------------><----------------|----><------>
// |left| (left maybe is negative)
// |<-->|
//
//
// O - The pen position for any time
//
// left (m_face->glyph->bitmap_left) - The horizontal distance from the current pen position to the glyph's left bbox edge.
//
// advance (m_face->glyph->advance.x >> 6) - The horizontal distance to increment (for left-to-right writing)
// or decrement (for right-to-left writing) the pen position after a
// glyph has been rendered when processing text
//
// width (bitmap->width) - The width of glyph
//
//
// Algorithm to compute size of the text bounding box:
//
// 1) Go through all symbols and shift pen position and save glyph parameters (left, advance, width)
// If left + pen position < 0 set left to 0. For example it's maybe happened
// if we print first letter 'J' or any other letter with negative 'left'
// We want to render glyph in pen position + left, so we must't allow it to be negative
//
// 2) If width == 0 we must to skip this symbol and don't save parameters for him.
// For example width == 0 for space sometimes
//
// 3) Also we compute max top and max bottom it's required for compute baseline
//
// 3) At the end we'll get the pen position for the symbol next to the last.
// See (1) on picture.
//
// 4) As we can see the last pen position is isn't horizontal size yet.
// We need to check if the glyph goes beyound the last position of the pen
// To do this we can:
// a) Return to the previous position -advance
// b) Shift on left value +left
// c) Shift on width of the last glyph
//
// Compare result position with pen position and choose max
//
// We can compute diff and check if diff > 0 pen.x += diff.
// See (2) on picture.
//
// 5) Return size. Complete!!!
//
// See also about freetype glyph metrics:
// https://www.freetype.org/freetype2/docs/glyphs/glyphs-3.html
GAPI_Assert(!FT_Set_Pixel_Sizes(m_face, fh, fh) &&
"Failed to set pixel size");
cv::Point pen(0, 0);
int max_bot = 0;
int max_top = 0;
int last_advance = 0;
int last_width = 0;
int last_left = 0;
for (const auto& wc : text)
{
GAPI_Assert(!FT_Load_Char(m_face, wc, FT_LOAD_RENDER) &&
"Failed to load char");
FT_Bitmap *bitmap = &(m_face->glyph->bitmap);
int left = m_face->glyph->bitmap_left;
int advance = (m_face->glyph->advance.x >> 6);
int width = bitmap->width;
// NB: Read (1) paragraph of algorithm description
if (pen.x + left < 0)
{
left = 0;
}
int bot = (m_face->glyph->metrics.height - m_face->glyph->metrics.horiBearingY) >> 6;
max_bot = std::max(max_bot, bot);
max_top = std::max(max_top, m_face->glyph->bitmap_top);
// NB: Read (2) paragraph of algorithm description
if (width != 0)
{
last_width = width;
last_advance = advance;
last_left = left;
}
pen.x += advance;
}
// NB: Read (4) paragraph of algorithm description
int diff = (last_width + last_left) - last_advance;
pen.x += (diff > 0) ? diff : 0;
if (baseline)
{
*baseline = max_bot;
}
return {pen.x, max_bot + max_top};
}
void cv::gapi::wip::draw::FTTextRender::Priv::putText(cv::Mat& mat,
const std::wstring& text,
const cv::Point& org,
int fh)
{
GAPI_Assert(!FT_Set_Pixel_Sizes(m_face, fh, fh) &&
"Failed to set pixel size");
cv::Point pen = org;
for (const auto& wc : text)
{
GAPI_Assert(!FT_Load_Char(m_face, wc, FT_LOAD_RENDER) &&
"Failed to load char");
FT_Bitmap *bitmap = &(m_face->glyph->bitmap);
// FIXME: Skip glyph, if size is 0
if (bitmap->rows == 0 || bitmap->width == 0) {
continue;
}
cv::Mat glyph(bitmap->rows, bitmap->width, CV_8UC1, bitmap->buffer, bitmap->pitch);
int left = m_face->glyph->bitmap_left;
int top = m_face->glyph->bitmap_top;
int advance = (m_face->glyph->advance.x >> 6);
if (pen.x + left < 0)
{
left = 0;
}
cv::Rect rect(pen.x + left, org.y - top, glyph.cols, glyph.rows);
auto roi = mat(rect);
roi += glyph;
pen.x += advance;
}
}
cv::gapi::wip::draw::FTTextRender::Priv::~Priv()
{
FT_Done_Face(m_face);
FT_Done_FreeType(m_library);
}
cv::gapi::wip::draw::FTTextRender::FTTextRender(const std::string& path)
: m_priv(new Priv(path))
{
}
cv::Size cv::gapi::wip::draw::FTTextRender::getTextSize(const std::wstring& text,
int fh,
int* baseline)
{
return m_priv->getTextSize(text, fh, baseline);
}
void cv::gapi::wip::draw::FTTextRender::putText(cv::Mat& mat,
const std::wstring& text,
const cv::Point& org,
int fh)
{
m_priv->putText(mat, text, org, fh);
}
#else
cv::Size cv::gapi::wip::draw::FTTextRender::getTextSize(const std::wstring&, int, int*)
{
cv::util::throw_error(std::runtime_error("Freetype not found"));
}
void cv::gapi::wip::draw::FTTextRender::putText(cv::Mat&, const std::wstring&, const cv::Point&, int)
{
cv::util::throw_error(std::runtime_error("Freetype not found"));
}
cv::gapi::wip::draw::FTTextRender::FTTextRender(const std::string&)
{
cv::util::throw_error(std::runtime_error("Freetype not found"));
}
#endif // HAVE_FREETYPE