使用Freetype2进行OpenGL字体渲染

我正在尝试使用OpenGL渲染freetype字体,遵循 http://en.wikibooks.org/wiki/OpenGL_Programming/Modern_OpenGL_Tutorial_Text_Rendering_02发布的示例.

我已经能够从字体生成纹理图集,创建着色器和创建四边形.我似乎被困在的是将纹理传递到着色器和/或为我的四边形获得正确的UV.现在一直在努力奋斗,真的需要帮助.

以下是我用来创建纹理图集的结构.

struct FontCharacter
    {
        float advanceX;
        float advanceY;

        float bitmapWidth;
        float bitmapHeight;

        float bitmapLeft;
        float bitmapTop;

        float uvOffsetX;
        float uvOffsetY;
    };

    struct FontTextureAtlas
    {
        GLuint texture;
        GLuint textureUniform;

        int width;
        int height;

        FontCharacter characters[128];

        FontTextureAtlas(FT_Face face,int h,GLuint tUniform)
        {
            FT_Set_Pixel_Sizes(face,h);
            FT_GlyphSlot glyphSlot = face->glyph;

            int roww = 0;
            int rowh = 0;
            width = 0;
            height = 0;

            memset(characters,sizeof(FontCharacter));

            for (int i = 32; i < 128; i++)
            {
                if (FT_Load_Char(face,i,FT_LOAD_RENDER))
                {
                    std::cout << "Loading character %c failedn",i;
                    continue;
                }

                if (roww + glyphSlot->bitmap.width + 1 >= MAX_WIDTH)
                {
                    width = std::fmax(width,roww);
                    height += rowh;
                    roww = 0;
                    rowh = 0;
                }

                roww += glyphSlot->bitmap.width + 1;
                rowh = std::fmax(rowh,glyphSlot->bitmap.rows);
            }

            width = std::fmax(width,roww);
            height += rowh;

            glGenTextures(1,&texture);

            if (glGetError() != GL_NO_ERROR)
            {
                std::cout << "glGenTextures failedn";
            }

            glActiveTexture(GL_TEXTURE0 + texture);

            if (glGetError() != GL_NO_ERROR)
            {
                std::cout << "glActiveTexture failedn";
            }

            glBindTexture(GL_TEXTURE_2D,texture);

            if (glGetError() != GL_NO_ERROR)
            {
                std::cout << "glBindTexture failedn";
            }

            glUniform1i(tUniform,0);
            textureUniform = tUniform;

            glTexImage2D(GL_TEXTURE_2D,GL_RED,width,height,GL_UNSIGNED_BYTE,0);

            if (glGetError() != GL_NO_ERROR)
            {
                std::cout << "glTexImage2D failedn";
            }

            glPixelStorei(GL_UNPACK_ALIGNMENT,1);

            if (glGetError() != GL_NO_ERROR)
            {
                std::cout << "glPixelStorei failedn";
            }

            glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAP_S,GL_CLAMP_TO_EDGE);

            if (glGetError() != GL_NO_ERROR)
            {
                std::cout << "glTexParameteri failedn";
            }

            glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_WRAP_T,GL_TEXTURE_MIN_FILTER,GL_LINEAR);

            if (glGetError() != GL_NO_ERROR)
            {
                std::cout << "glTexParameteri failedn";
            }

            glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);

            if (glGetError() != GL_NO_ERROR)
            {
                std::cout << "glTexParameteri failedn";
            }


            int ox = 0;
            int oy = 0;

            rowh = 0;

            for (int i = 32; i < 128; i++)
            {
                if (FT_Load_Char(face,i;
                    continue;
                }

                if (ox + glyphSlot->bitmap.width + 1 >= MAX_WIDTH) 
                {
                    oy += rowh;
                    rowh = 0;
                    ox = 0;
                }

                glTexSubImage2D(GL_TEXTURE_2D,ox,oy,glyphSlot->bitmap.width,glyphSlot->bitmap.rows,glyphSlot->bitmap.buffer);

                if (glGetError() != GL_NO_ERROR)
                {
                    std::cout << "BORKED AGAINn";
                }

                characters[i].advanceX = glyphSlot->advance.x >> 6;
                characters[i].advanceY = glyphSlot->advance.y >> 6;

                characters[i].bitmapWidth = glyphSlot->bitmap.width;
                characters[i].bitmapHeight = glyphSlot->bitmap.rows;

                characters[i].bitmapLeft = glyphSlot->bitmap_left;
                characters[i].bitmapTop = glyphSlot->bitmap_top;

                characters[i].uvOffsetX = ox / (float)width;
                characters[i].uvOffsetY = oy / (float)height;

                rowh = std::fmax(rowh,glyphSlot->bitmap.rows);
                ox += glyphSlot->bitmap.width + 1;
            }

            std::cout << "Generated a " << width << "x " << height << " (" << width * height / 1024 << " kb) texture atlas.n";
        }

        ~FontTextureAtlas()
        {
            glDeleteTextures(1,&texture);
        }

渲染器中使用的局部变量和函数头

class RenderCore
{    
FT_Library library;
            FT_Face face;
            FontTextureAtlas* a48;
            FontTextureAtlas* a24;
            FontTextureAtlas* a12;
            GLuint vbo;
            GLuint vao;
            GLuint m_posUV;
            GLuint m_colorIN;
            GLuint m_texture;

            int InitFT();
            void RenderText(const char* text,FontTextureAtlas* atlas,float x,float y,float sx,float sy);
}

这是我加载字体的地方.

int RenderCore::InitFT()
{
    if (FT_Init_FreeType(&library))
    {
        std::cout << "Could not Initialize freetype library.n";
        return 0;
    }

    /* Load a font */
    if (FT_New_Face(library,"assets/Fonts/arialbd.ttf",&face))
    {
        std::cout << "Could not open font assets/Fonts/DentonBeta2.ttfn";
        return 0;
    }

    m_shaderManager->CreateProgram("Text");
    m_shaderManager->LoadShader("shaders/Text.vertex","TextVS",GL_VERTEX_SHADER);
    m_shaderManager->LoadShader("shaders/Text.fragment","TextFS",GL_FRAGMENT_SHADER);
    m_shaderManager->AttachShader("TextVS","Text");
    m_shaderManager->AttachShader("TextFS","Text");
    m_shaderManager->LinkProgram("Text");
    m_shaderManager->UseProgram("Text");
    m_shaderManager->UseProgram("Text");

    m_colorIN = m_shaderManager->GetUniformLocation("Text","inputColor");
    m_texture = m_shaderManager->GetUniformLocation("Text","texture");


    // Create the vertex buffer object
    glGenBuffers(1,&vbo);
    glGenVertexArrays(1,&vao);
    /* Create texture atlasses for several font sizes */
    a48 = new FontTextureAtlas(face,48,m_texture);
    a24 = new FontTextureAtlas(face,24,m_texture);
    a12 = new FontTextureAtlas(face,12,m_texture);
}

渲染功能.

void RenderCore::RenderText(const char* text,float sy)
    {
        m_shaderManager->UseProgram("Text");

        const unsigned char* p;

        std::vector<glm::vec4> coords;

        int c = 0;

        for (p = (const unsigned char*)text; *p; p++)
        {
            float x2 = x + atlas->characters[*p].bitmapLeft * sx;
            float y2 = -y - atlas->characters[*p].bitmapTop * sy;
            float w = atlas->characters[*p].bitmapWidth * sx;
            float h = atlas->characters[*p].bitmapHeight * sy;

            x += atlas->characters[*p].advanceX * sx;
            y += atlas->characters[*p].advanceY * sy;

            if (!w || !h)
                continue;


            coords.push_back(
                glm::vec4(
                x2,-y2,atlas->characters[*p].uvOffsetX,atlas->characters[*p].uvOffsetY)
                );


            coords.push_back(
                glm::vec4(
                x2 + w,atlas->characters[*p].uvOffsetX + atlas->characters[*p].bitmapWidth / atlas->width,atlas->characters[*p].uvOffsetY)
                );



            coords.push_back(
                glm::vec4(
                x2,-y2 - h,atlas->characters[*p].uvOffsetY + atlas->characters[*p].bitmapHeight / atlas->height)
                );



            coords.push_back(
                glm::vec4(
                x2 + w,atlas->characters[*p].uvOffsetY)
                );


            coords.push_back(
                glm::vec4(
                x2,atlas->characters[*p].uvOffsetY + atlas->characters[*p].bitmapHeight / atlas->height)
                );


            coords.push_back(
                glm::vec4(
                x2 + w,atlas->characters[*p].uvOffsetY + atlas->characters[*p].bitmapHeight / atlas->height)
                );
        }

        glEnable(GL_BLEND);
        glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);

        glActiveTexture(GL_TEXTURE0 + atlas->texture);
        glUniform1i(atlas->textureUniform,0);
        glBindTexture(GL_TEXTURE_2D,atlas->texture);

        m_shaderManager->SetUniform(1,glm::vec4(0,1,1),m_colorIN);

        glBindBuffer(GL_ARRAY_BUFFER,vbo);
        glBufferData(GL_ARRAY_BUFFER,coords.size() * sizeof(glm::vec4),coords.data(),GL_DYNAMIC_DRAW);

        //Generate VAO
        glBindVertexArray(vao);

        //Position
        glEnableVertexAttribArray(0);
        glVertexAttribPointer(0,4,GL_FLOAT,GL_FALSE,sizeof(glm::vec4),(void*)0);

        glBindVertexArray(vao);
        glDrawArrays(GL_TRIANGLE_STRIP,coords.size());

        glDisableVertexAttribArray(0);
        m_shaderManager->ResetProgram();
    }

顶点着色器

#version 440

in vec4 pos_uv;
out vec2 uv;

void main()
{
    gl_Position = vec4(pos_uv.xy,1);
    uv = pos_uv.zw;
}

片段着色器

#version 440

    in vec2 uv;
    uniform sampler2D texture;
    uniform vec4 inputColor;

    out vec4 color;

    void main()
    {
        color = vec4(inputColor.rgb,texture2D(texture,uv).a);
    }

使用gDebugger,我可以看到纹理图谱已经正确生成,VBO似乎也很好.结果只是屏幕上的一堆正方形,但我真的不知道为什么.我认为将纹理传递到着色器可能会出现问题,除alpha通道外的所有通道都是空的,alpha始终为1.