使用FreeType库创建文本位图以在OpenGL 3.x中绘制

Question

At the moment I not too sure where my problem is. I can draw loaded images as textures no problem, however when I try to generate a bitmap with a char on it I just get a black box.

I am confident that the problem is when I generate and upload the texture.

Here is the method for that; the top section of the if statement just draws an texture of a image loaded from file (res/texture.jpg) and that draws perfectly. And the else part of the if statement will try to generate and upload a texture with the char (variable char enter) on.

Source Code, I will add shaders and more of the C++ if needed but they work fine for the image.

    void uploadTexture()
    {
        if(enter=='/'){

            // Draw the image.
            GLenum imageFormat;
            glimg::SingleImage image = glimg::loaders::stb::LoadFromFile("res/texture.jpg")->GetImage(0,0,0);
            glimg::OpenGLPixelTransferParams params =  glimg::GetUploadFormatType(image.GetFormat(), 0);
            imageFormat = glimg::GetInternalFormat(image.GetFormat(),0);

            glGenTextures(1,&textureBufferObject);
            glBindTexture(GL_TEXTURE_2D, textureBufferObject);

            glimg::Dimensions dimensions = image.GetDimensions();
            cout << "Texture dimensions w "<< dimensions.width << endl;
            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB8, dimensions.width, dimensions.height, 0, params.format, params.type, image.GetImageData());
        }else
        {
            // Draw the char useing the FreeType Lib
            FT_Init_FreeType(&ft);
            FT_New_Face(ft, "arial.ttf", 0, &face);
            FT_Set_Pixel_Sizes(face, 0, 48);

            FT_GlyphSlot g = face->glyph;


            glGenTextures(1,&textureBufferObject);
            glBindTexture(GL_TEXTURE_2D, textureBufferObject);

            glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

            FT_Load_Char(face, enter, FT_LOAD_RENDER);
            FT_Bitmap theBitmap = g->bitmap;

            int BitmapWidth = g->bitmap.width;
            int BitmapHeight = g->bitmap.rows;



            cout << "draw char - " << enter << endl;
            cout << "g->bitmap.width - " << g->bitmap.width << endl;
            cout << "g->bitmap.rows - " << g->bitmap.rows << endl;

            int TextureWidth =roundUpToNextPowerOfTwo(g->bitmap.width);
            int TextureHeight =roundUpToNextPowerOfTwo(g->bitmap.rows);

            cout << "texture width x height - " << TextureWidth <<" x " << TextureHeight << endl;

            GLubyte* TextureBuffer = new GLubyte[ TextureWidth * TextureWidth ];
            for(int j = 0; j < TextureHeight; ++j)
            {
                for(int i = 0; i < TextureWidth; ++i)
                {
                    TextureBuffer[ j*TextureWidth + i ] = (j >= BitmapHeight || i >= BitmapWidth ? 0 : g->bitmap.buffer[ j*BitmapWidth + i ]);
                }
            }

            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB8, TextureWidth, TextureHeight, 0, GL_RGB8, GL_UNSIGNED_BYTE, TextureBuffer);
        }

    } 

Answer 1

I'm not sure about the OpenGL part, but your algorithm to process FT bitmap is not correct. The number of bytes of each row in FT bitmap is bitmap->pitch . The number of each pixel also depends on which render mode your are loading the character. For example, if bitmap->pixel_mode is FT_PIXEL_MODE_LCD , each pixel is encoded as 3 bytes, in order of R, G, B and the values are actually the alpha mask value, while if the pixel mode is FT_PIXEL_MODE_GRAY , each pixel is 1 byte and the values are the gray level.

Take a look at http://freetype.sourceforge.net/freetype2/docs/reference/ft2-basic_types.html#FT_Bitmap

Answer 2

The very first thing I'd do would be to look at the return codes that Freetype gives to pretty much ALL the FT_* functions.

That's good practice anyway, but if you have a problem it should narrow it down substantially.