如何使用GDI渲染8位索引位图？

Question

I'm trying to render a freetype's glyph to a window using windows GDI. It seems the bitmap generated by freetype is 8bit index bitmap or something, because in its official tutorial example4.cpp, it use Qt to render the glyph as follows:

error = FT_Render_Glyph(m_face->glyph,
                    FT_RENDER_MODE_NORMAL);

            QImage glyphImage(m_face->glyph->bitmap.buffer,
                m_face->glyph->bitmap.width,
                m_face->glyph->bitmap.rows,
                m_face->glyph->bitmap.pitch,
                QImage::Format_Indexed8);

            /*painter.translate(m_glyphRect.x(),
                m_glyphRect.y());*/

            QVector<QRgb> colorTable;
            for (int i = 0; i < 256; ++i)
                colorTable << qRgba(0, 0, 0, i);
            glyphImage.setColorTable(colorTable);

            painter.drawImage(QPoint(0, 0),
                glyphImage);

So I try to render it using gdi as follows:

BITMAPINFO* pBmi = (BITMAPINFO*)malloc(sizeof(BITMAPINFO) + sizeof(RGBQUAD) * 255);
            BITMAPINFOHEADER &bmh = pBmi->bmiHeader;
            bmh.biSize = sizeof(BITMAPINFOHEADER);
            bmh.biBitCount = 8;
            bmh.biCompression = BI_RGB;
            bmh.biPlanes = 1;
            RGBQUAD* palette = &pBmi->bmiColors[0];
            for (int i = 0; i < 256; ++i) {
                RGBQUAD rgb = {0};
                palette[i] = rgb;
            }

            //assert(pBm->bitmap);
            bmh.biWidth = pBm->bitmap.width;
            bmh.biHeight =  - pBm->bitmap.rows;
            StretchDIBits(hdc, 200, 200, pBm->bitmap.width, pBm->bitmap.rows, 0, 0, pBm->bitmap.width, pBm->bitmap.rows, pBm->bitmap.buffer, 
                pBmi, DIB_PAL_COLORS, SRCCOPY);

Then I try to use GDI+ to render, but failed too.

error = FT_Render_Glyph(m_face->glyph, FT_RENDER_MODE_NORMAL);
            Bitmap bitmap(pBm->bitmap.width, pBm->bitmap.rows, pBm->bitmap.pitch, PixelFormat8bppIndexed, pBm->bitmap.buffer);
            //Bitmap bitmap(pBm->bitmap.width, pBm->bitmap.rows, 64, PixelFormat8bppIndexed, pBm->bitmap.buffer);
            ColorPalette* pal = (ColorPalette*)malloc(sizeof(ColorPalette) + 255 * sizeof(ARGB));
            pal->Flags = PaletteFlagsGrayScale;
            pal->Count = 256;
            for (int i = 0; i <= 255; i++) {
                pal->Entries[i] = Color::MakeARGB(i, 0, 0, 0);
            }
            bitmap.SetPalette(pal);
            Graphics graphics(hdc);
            graphics.DrawImage(&bitmap, 100, 100);

Could you please tell me, how to render 8bit per pixel indexed bitmap in Windows using GDI/GDI+. Thanks.

Answer 1

Just as a note here:

        hdc = BeginPaint(hWnd, &ps);

        assert(Draw());

        FT_GlyphSlot &pBm = m_face->glyph;

        //output by console
        {
            printf("\n");
            for (int j = 0; j < pBm->bitmap.rows; j++) {
                printf("\n");
                for (int i = 0; i < pBm->bitmap.width; i++) 
                    printf("%2x", pBm->bitmap.buffer[j * pBm->bitmap.width + i]);
            }
        }

        //output by gdi+
        {
            Bitmap *pBitmap = NULL;
            LPBYTE pBuffer = NULL;      
            int stride = (pBm->bitmap.pitch + 3) / 4 * 4;
            if (stride != pBm->bitmap.pitch)
            {
                pBuffer = new BYTE[stride * pBm->bitmap.rows];
                memset(pBuffer, 0, stride * pBm->bitmap.rows);
                for (int i = 0; i < pBm->bitmap.rows; i++)
                    for (int j = 0; j < pBm->bitmap.width; j++)
                        pBuffer[i * stride + j] = pBm->bitmap.buffer[i * pBm->bitmap.width + j];
            } else
            {
                pBuffer = pBm->bitmap.buffer;
            }
            pBitmap = new Bitmap(pBm->bitmap.width, pBm->bitmap.rows, stride, PixelFormat8bppIndexed, pBuffer);
            ColorPalette *pPalette = (ColorPalette*)malloc(sizeof(ColorPalette) + 255 * sizeof(ARGB));
            pPalette->Count = 256;
            pPalette->Flags = PaletteFlagsGrayScale;
            ARGB* pColor = &pPalette->Entries[0];
            for (int i = 0; i < 256; i++)
                pColor[i] = Color::MakeARGB(i, 0x00, 0x00, 0x00);
            assert(pBitmap->GetLastStatus() == Ok);
            pBitmap->SetPalette(pPalette);
            assert(pBitmap->GetLastStatus() == Ok);
            Graphics graphics(hdc);
            graphics.DrawImage(pBitmap, 300, 300);

            free(pPalette);
            delete pBitmap;

            //draw with gdi
            {
                BITMAPINFO* pBmi = (BITMAPINFO*)malloc(sizeof(BITMAPINFO) + sizeof(RGBQUAD) * 255);
                memset(pBmi, 0, sizeof(BITMAPINFO));
                BITMAPINFOHEADER &bmh = pBmi->bmiHeader;
                bmh.biSize = sizeof(BITMAPINFOHEADER);
                bmh.biBitCount = 8;
                bmh.biCompression = BI_RGB;
                bmh.biPlanes = 1;
                RGBQUAD* palette = &pBmi->bmiColors[0];
                for (int i = 0; i < 256; ++i) 
                {
                    RGBQUAD rgb = {0};
                    rgb.rgbRed =  ~i;
                    rgb.rgbGreen =  ~i;
                    rgb.rgbBlue =  ~i;
                    palette[i] = rgb;
                }
                bmh.biWidth = stride;
                bmh.biHeight =  - pBm->bitmap.rows;
                StretchDIBits(hdc, 200, 200, stride, pBm->bitmap.rows, 0, 0, stride, pBm->bitmap.rows, pBuffer, 
                    pBmi, DIB_RGB_COLORS, SRCCOPY);

                if (pBmi)
                    free(pBmi);

                if (pBuffer != pBm->bitmap.buffer)
                    delete [] pBuffer;

                /*bmh.biWidth = pBm->bitmap.width;
                bmh.biHeight =  - pBm->bitmap.rows;
                StretchDIBits(hdc, 200, 200, pBm->bitmap.width, pBm->bitmap.rows, 0, 0, pBm->bitmap.width, pBm->bitmap.rows, pBm->bitmap.buffer, 
                    pBmi, DIB_PAL_COLORS, SRCCOPY);*/
            }

        }
        EndPaint(hWnd, &ps);

Two points:
1) as Mark Randsom and paulsm4 said color palette is mandantory.
2) align by 4.

Answer 2

The Qt example you give creates a color palette that's all black, with the transparency varying with the intensity. The palette you're using with GDI is all black, period. You need to vary the color.