3
這真是太遺憾了，我從來沒有在我的應用程序中從未獲得過堅實的字體渲染系統。所以我決定結束這個。實現距離場字體渲染
雖然我在尋找字體渲染的例子，但我碰巧進入了這個每個人都稱讚的valve paper。
但是我缺乏經驗和知識來完成這個。
這裏是什麼，我做了總結：
首先，使用對FreeType2庫，我裝一個字符（「A」）到存儲爲位圖。
unsigned char u8Character = 'A';
int32_t u32Character = 0;
utf8::utf8to32(&u8Character, &u8Character + 1, &u32Character);
FT_Set_Char_Size(face, 0, 64 * 64, 300, 300);
FT_Load_Char(face, u32Character, FT_LOAD_RENDER);
其次，我計算距離場從位圖來生成浮點數地圖的每個像素切比雪夫距離。
注意：老實說，我不知道該怎麼做。下面的算法是完整的猜測。
template <typename input_type, typename output_type>
output_type chebyshev_distance(input_type from_x
, input_type from_y
, input_type to_x
, input_type to_y)
{
input_type dx = std::abs(to_x - from_x);
input_type dy = std::abs(to_y - from_y);
return static_cast<output_type>(dx > dy ? dx : dy);
}
void GenerateSigendDistanceFieldFrom(const unsigned char* inputBuffer
, int width
, int height
, float* outputBuffer
, bool normalize = false)
{
for (int iy = 0; iy < height; ++iy)
{
for (int ix = 0; ix < width; ++ix)
{
int index = iy*width + ix;
unsigned char value = inputBuffer[index];
int indexMax = width*height;
int indexMin = 0;
int far = width > height ? width : height;
bool found = false;
for (int distance = 1; distance < far; ++distance)
{
int xmin = (ix - distance) >= 0 ? ix - distance : 0;
int ymin = (iy - distance) >= 0 ? iy - distance : 0;
int xmax = (ix + distance) < width ? ix + distance+1 : width;
int ymax = (iy + distance) < height ? iy + distance+1 : height;
int x = xmin;
int y = ymin;
auto fCompareAndFill = [&]() -> bool
{
if (value != inputBuffer[y*width + x])
{
outputBuffer[index] = chebyshev_distance<int, float>(ix, iy, x, y);
if (value < 0xff/2) outputBuffer[index] *= -1;
//outputBuffer[index] = distance;
return true;
}
return false;
};
while (x < xmax)
{
if (fCompareAndFill())
{
found = true;
break;
}
++x;
}
--x;
if (found == true){ break; }
while (y < ymax)
{
if (fCompareAndFill())
{
found = true;
break;
}
++y;
}
--y;
if (found == true){ break; }
while (x >= xmin)
{
if (fCompareAndFill())
{
found = true;
break;
}
--x;
}
++x;
if (found == true){ break; }
while (y >= ymin)
{
if (fCompareAndFill())
{
found = true;
break;
}
--y;
}
if (found == true){ break; }
} // for(int distance = 1; distance < far; ++distance)
} // for(int ix = 0; ix < width; ++ix)
} // for(int iy = 0; iy < height; ++iy)
if(normalize)
{
float min = outputBuffer[0];
float max = outputBuffer[0];
for(int i = 0; i < width*height; ++i)
{
if(outputBuffer[i] < min)
min = outputBuffer[i];
if(outputBuffer[i] > max)
max = outputBuffer[i];
}
float denominator = (max - min);
float newMin = min/denominator;
for(int i = 0; i < width*height; ++i)
{
outputBuffer[i] /= denominator;
outputBuffer[i] -= newMin;
}
}
} // GenerateSigendDistanceFieldFrom
第三，作爲一個測試，我將這個字符的紋理渲染到800x600的整個屏幕上，看看它們是如何展開的。紋理採樣「GL_LINEAR」結果很糟糕。
！1！將Alpha渲染爲紅色值。
const GLchar fssource[] =
"#version 440 \n"
"out vec4 v_color;"
"in vec2 v_uv;"
"uniform sampler2D u_texture;"
"void main()"
"{"
" float mask = texture(u_texture, v_uv).a;"
" v_color = vec4(mask,0,0,1);"
"}"
;
！2！渲染文本。閾值用於α-是0.5
const GLchar fssource[] =
"#version 440 \n"
"out vec4 v_color;"
"in vec2 v_uv;"
"uniform sampler2D u_texture;"
"void main()"
"{"
" vec4 result = vec4(1,1,1,1);"
" float mask = texture(u_texture, v_uv).a;"
" if(mask >= 0.5) { result.a = 1; }\n"
" else { result.a = 0; }\n"
" v_color = result;"
"}"
！3！渲染文本。閾值用於α-是0.7
const GLchar fssource[] =
"#version 440 \n"
"out vec4 v_color;"
"in vec2 v_uv;"
"uniform sampler2D u_texture;"
"void main()"
"{"
" vec4 result = vec4(1,1,1,1);"
" float mask = texture(u_texture, v_uv).a;"
" if(mask >= 0.7) { result.a = 1; }\n"
" else { result.a = 0; }\n"
" v_color = result;"
"}"
的字體看起來顛簸，顯然距離場太亮。算法應該用0.5閾值工作。 不僅結果不正確，距離場的產生花費太多時間。因此，我無法使用高分辨率圖像作爲輸入。
在這裏，我正在做一些明顯錯誤的事情，但似乎我自己想出如何生成正確的結果。
但是，請幫助我，如果你知道我做錯了什麼。
下面是整個源文件：
#include <iostream>
#include <iomanip>
#include <algorithm>
#include <fstream>
#include <vector>
#include <cstdint>
#include <climits>
#include "ft2build.h"
#include FT_FREETYPE_H
#include "../utf8_v2_3_4/Source/utf8.h"
#include <SDL.h>
#include "../Glew/glew.h"
#include <gl/GL.h>
#undef main
template <typename input_type, typename output_type>
output_type chebyshev_distance(input_type from_x
, input_type from_y
, input_type to_x
, input_type to_y)
{
input_type dx = std::abs(to_x - from_x);
input_type dy = std::abs(to_y - from_y);
return static_cast<output_type>(dx > dy ? dx : dy);
}
void GenerateSigendDistanceFieldFrom(const unsigned char* inputBuffer
, int width
, int height
, float* outputBuffer
, bool normalize = false)
{
for (int iy = 0; iy < height; ++iy)
{
for (int ix = 0; ix < width; ++ix)
{
int index = iy*width + ix;
unsigned char value = inputBuffer[index];
int indexMax = width*height;
int indexMin = 0;
int far = width > height ? width : height;
bool found = false;
for (int distance = 1; distance < far; ++distance)
{
int xmin = (ix - distance) >= 0 ? ix - distance : 0;
int ymin = (iy - distance) >= 0 ? iy - distance : 0;
int xmax = (ix + distance) < width ? ix + distance+1 : width;
int ymax = (iy + distance) < height ? iy + distance+1 : height;
int x = xmin;
int y = ymin;
auto fCompareAndFill = [&]() -> bool
{
if (value != inputBuffer[y*width + x])
{
outputBuffer[index] = chebyshev_distance<int, float>(ix, iy, x, y);
if (value < 0xff/2) outputBuffer[index] *= -1;
//outputBuffer[index] = distance;
return true;
}
return false;
};
while (x < xmax)
{
if (fCompareAndFill())
{
found = true;
break;
}
++x;
}
--x;
if (found == true){ break; }
while (y < ymax)
{
if (fCompareAndFill())
{
found = true;
break;
}
++y;
}
--y;
if (found == true){ break; }
while (x >= xmin)
{
if (fCompareAndFill())
{
found = true;
break;
}
--x;
}
++x;
if (found == true){ break; }
while (y >= ymin)
{
if (fCompareAndFill())
{
found = true;
break;
}
--y;
}
if (found == true){ break; }
} // for(int distance = 1; distance < far; ++distance)
} // for(int ix = 0; ix < width; ++ix)
} // for(int iy = 0; iy < height; ++iy)
if(normalize)
{
float min = outputBuffer[0];
float max = outputBuffer[0];
for(int i = 0; i < width*height; ++i)
{
if(outputBuffer[i] < min)
min = outputBuffer[i];
if(outputBuffer[i] > max)
max = outputBuffer[i];
}
float denominator = (max - min);
float newMin = min/denominator;
for(int i = 0; i < width*height; ++i)
{
outputBuffer[i] /= denominator;
outputBuffer[i] -= newMin;
}
}
} // GenerateSigendDistanceFieldFrom
namespace
{
SDL_Window* window = NULL;
SDL_Surface* screenSurface = NULL;
FT_Library freetype;
FT_Face face;
SDL_GLContext glContext;
GLuint glProgram = 0;
GLuint vbo = 0;
GLuint vao = 0;
GLuint glTexture = 0;
}
GLuint MakeShader(GLenum shaderType, const char* source, int slen)
{
auto shader = glCreateShader(shaderType);
glShaderSource(shader, 1, (const GLchar**)&source, &slen);
glCompileShader(shader);
GLint success;
glGetShaderiv(shader, GL_COMPILE_STATUS, &success);
if (success == GL_FALSE)
{
std::vector<GLchar> glInfoLogBuffer;
int len;
glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &len);
glInfoLogBuffer.resize(len + 1);
GLsizei outlen;
glGetShaderInfoLog(shader, glInfoLogBuffer.size(), &outlen, glInfoLogBuffer.data());
glInfoLogBuffer.back() = 0;
std::cout << glInfoLogBuffer.data() << std::endl;
return 0;
}
return shader;
}
GLuint MakeProgram(GLuint vshader, GLuint fshader)
{
auto program = glCreateProgram();
glAttachShader(program, vshader);
glAttachShader(program, fshader);
glLinkProgram(program);
GLint success;
glGetProgramiv(program, GL_LINK_STATUS, &success);
if(success == GL_FALSE)
{
int len;
glGetProgramiv(program, GL_INFO_LOG_LENGTH, &len);
std::vector<GLchar> buffer;
buffer.resize(len+1);
buffer.back() = 0;
glGetProgramInfoLog(program, buffer.size(), &len, buffer.data());
std::cout << buffer.data() << std::endl;
return 0;
}
return program;
}
int Initialize()
{
if (SDL_Init(SDL_INIT_VIDEO) < 0)
{
std::cout << "SDL could not initialize!";
return -1;
}
window = SDL_CreateWindow("My Window", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, 800, 600, SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN);
if (!window)
{
std::cout << "Window could not be created!";
return -1;
}
screenSurface = SDL_GetWindowSurface(window);
SDL_FillRect(screenSurface, 0, SDL_MapRGB(screenSurface->format, 0xFF, 0xFF, 0xFF));
SDL_UpdateWindowSurface(window);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 1);
SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
glContext = SDL_GL_CreateContext(window);
SDL_GL_SetSwapInterval(1);
GLenum glError = glewInit();
if(glError != GLEW_OK)
{
std::cout << "Failed to initialize glew" << std::endl;
return -1;
}
// ----------------------
// Vertex Shader
const GLchar vssource[] =
"#version 440 \n"
"layout(location=0) in vec3 a_position;"
"layout(location=1) in vec2 a_uv;"
"out vec2 v_uv;"
"void main()"
"{"
" gl_Position = vec4(a_position,1);"
" v_uv = a_uv;"
"}\n"
;
auto vshader = MakeShader(GL_VERTEX_SHADER, vssource, _countof(vssource));
// --------------------
// Fragment Shader
//const GLchar fssource[] =
// "#version 440 \n"
// "out vec4 v_color;"
// "in vec2 v_uv;"
// "uniform sampler2D u_texture;"
// "void main()"
// "{"
// " float mask = texture(u_texture, v_uv).a;"
// " v_color = vec4(mask,0,0,1);"
// "}"
//;
const GLchar fssource[] =
"#version 440 \n"
"out vec4 v_color;"
"in vec2 v_uv;"
"uniform sampler2D u_texture;"
"void main()"
"{"
" vec4 result = vec4(1,1,1,1);"
" float mask = texture(u_texture, v_uv).a;"
" if(mask >= 0.7) { result.a = 1; }\n"
" else { result.a = 0; }\n"
" v_color = result;"
"}"
;
auto fshader = MakeShader(GL_FRAGMENT_SHADER, fssource, _countof(fssource));
// --------------------
// Shader Program
glProgram = MakeProgram(vshader, fshader);
// --------------------
// Vertex Buffer Object
float vb[] =
{
-1, -1, 0,
1, -1, 0,
-1, 1, 0,
1, -1, 0,
1, 1, 0,
-1, 1, 0,
0, 0,
1, 0,
0, 1,
1, 0,
1, 1,
0, 1,
};
glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, sizeof(vb), vb, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
// --------------------
// Vertex Array Object
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, (const GLvoid*)(sizeof(float)*18));
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);
//
// Freetype
//
FT_Error error = FT_Init_FreeType(&freetype);
if (error)
{
std::cout << "FreeType: error occured with error code: " << error << std::endl;
}
error = FT_New_Face(freetype, "C:/Windows/Fonts/Arial.ttf", 0, &face);
if (error)
{
std::cout << "FreeType: error occured with error code: " << error << std::endl;
}
error = FT_Set_Char_Size(face, 0, 64 * 64, 300, 300);
if (error)
{
std::cout << "FreeType: error occured with error code: " << error << std::endl;
}
unsigned char u8Character = 'A';
int32_t u32Character = 0;
utf8::utf8to32(&u8Character, &u8Character + 1, &u32Character);
error = FT_Load_Char(face, u32Character, FT_LOAD_RENDER);
if (error)
{
std::cout << "FreeType: error occured with error code: " << error << std::endl;
}
auto bitmap = face->glyph->bitmap;
const int width = bitmap.width;
const int height = bitmap.rows;
const int size = width*height;
std::vector<float> outputBuffer;
outputBuffer.resize(size);
GenerateSigendDistanceFieldFrom(face->glyph->bitmap.buffer, width, height, outputBuffer.data(), true);
std::ofstream ofs("testout.txt");
for (int i = 0; i < height; ++i)
{
for (int j = 0; j < width; ++j)
{
ofs << bitmap.buffer[i*width + j] << ' ';
}
ofs << std::endl;
}
ofs << std::endl;
for (int i = 0; i < height; ++i)
{
for (int j = 0; j < width; ++j)
{
ofs << std::setw(6) << std::setprecision(2) << std::fixed << outputBuffer[i*width + j];
}
ofs << std::endl;
}
// ----
// --------------------
// Texture
std::vector<float> invertY;
invertY.reserve(size);
for(int i = height-1; i >= 0; --i)
{
for(int j = 0; j < width; ++j)
{
invertY.push_back(outputBuffer[i*width+j]);
}
}
glGenTextures(1, &glTexture);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, glTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, width, height, 0, GL_ALPHA, GL_FLOAT, invertY.data());
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glGenerateMipmap(GL_TEXTURE_2D);
glClearColor(0.5f,0.5f,1.0f,1.0f);
return 0;
}
void Release()
{
SDL_DestroyWindow(window);
SDL_Quit();
}
int main(int argc, char* argv[])
{
Initialize();
bool quit = false;
while(!quit)
{
SDL_Event e;
if(SDL_PollEvent(&e) != 0)
{
if (e.type == SDL_QUIT)
{
quit = true;
}
} // if(SDL_PollEvent(&e) != 0)
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glUseProgram(glProgram);
GLint loc = glGetUniformLocation(glProgram, "u_texture");
glUniform1i(loc, 0);
glBindVertexArray(vao);
glDrawArrays(GL_TRIANGLES, 0, 6);
glBindVertexArray(0);
glUseProgram(0);
SDL_GL_SwapWindow(window);
} // while(!quit)
Release();
return 0;
}
感謝您的回覆。的確，使用更高分辨率的輸入有助於獲得更好的視覺效果而不會出現鋸齒。根據freetype教程，FT_Set_Char_Size的大小以像素單位（1/64像素）爲單位，但實際上，我得到的實際寬度，高度範圍在100到200之間...這是另一個問題。但我仍然需要更快的算法來計算距離場來縮放圖像。 – user2883715