全网首发：JDK绘制文字：四、绘制文字的具体函数分析

　　经历过一番分析，我们对绘制的相关工作大体了解了。现在要问：具体绘制函数是哪个？代码内容是怎样的？

• 预备知识

　　绘制文字，说到底就是把字体文件中对应的图像数据画上去（代码上就是复制到某个缓冲区）。

　　图像，包含几个关键信息：图像宽和高，格式（每个像素是bit，还是byte）。结合宽和格式，就产生了一个每行几个字节的信息。

• ByteBinary1Bit.c

DEFINE_BYTE_BINARY_SOLID_DRAWGLYPHLIST(ByteBinary1Bit)

• DEFINE_BYTE_BINARY_SOLID_DRAWGLYPHLIST(AnyByteBinary.h)

在LoopMacros.h中有一个类似的DEFINE_SOLID_DRAWGLYPHLIST宏定义。二者几乎一样。

#define DEFINE_BYTE_BINARY_SOLID_DRAWGLYPHLIST(DST) \
void NAME_SOLID_DRAWGLYPHLIST(DST)(SurfaceDataRasInfo *pRasInfo, \
                                   ImageRef *glyphs, \
                                   jint totalGlyphs, jint fgpixel, \
                                   jint argbcolor, \
                                   jint clipLeft, jint clipTop, \
                                   jint clipRight, jint clipBottom, \
                                   NativePrimitive *pPrim, \
                                   CompositeInfo *pCompInfo) \
{ \
    jint glyphCounter; \
    jint scan = pRasInfo->scanStride; \
    DST ## DataType *pPix; \
\
    //totalGlyphs: 本次绘制几个文字
    for (glyphCounter = 0; glyphCounter < totalGlyphs; glyphCounter++) { \
        DeclareDrawGlyphListClipVars(pixels, rowBytes, width, height, \
                                     left, top, right, bottom) \
        ClipDrawGlyphList(DST, pixels, 1, rowBytes, width, height, \
                          left, top, right, bottom, \
                          clipLeft, clipTop, clipRight, clipBottom, \
                          glyphs, glyphCounter, continue) \
        pPix = PtrCoord(pRasInfo->rasBase,left,DST ## PixelStride,top,scan); \
\
        do { \
            Declare ## DST ## InitialLoadVars(pRasInfo, pPix, DstPix, left) \
            jint x = 0; \
            do { \
                InitialLoad ## DST(pPix, DstPix); \
                if (pixels[x]) { \
                    Store ## DST ## PixelData(pPix, 0, fgpixel, DstPix); \
                } \
                ShiftBits ## DST(DstPix); \
            } while (++x < width); \
            FinalStore ## DST(pPix, DstPix); \
            pPix = PtrAddBytes(pPix, scan); \
            // rowBytes就是每行几个字节
            pixels += rowBytes; \
        } while (--height > 0); \
    } \
}

终于，我们找到了真正的绘制函数。

• DeclareDrawGlyphListClipVars(LoopMacros.h)

声明一些局部变量。

#define DeclareDrawGlyphListClipVars(PIXELS, ROWBYTES, WIDTH, HEIGHT, \
                                     LEFT, TOP, RIGHT, BOTTOM) \
    const jubyte * PIXELS; \
    int ROWBYTES; \
    int LEFT, TOP; \
    int WIDTH, HEIGHT; \
    int RIGHT, BOTTOM;

• ClipDrawGlyphList(LoopMacros.h)

初始化声明的局部变量。这里可以看到width/height是如何初始化的。

#define ClipDrawGlyphList(DST, PIXELS, BYTESPERPIXEL, ROWBYTES, WIDTH, HEIGHT,\
                          LEFT, TOP, RIGHT, BOTTOM, \
                          CLIPLEFT, CLIPTOP, CLIPRIGHT, CLIPBOTTOM, \
                          GLYPHS, GLYPHCOUNTER, NULLGLYPHCODE) \
    PIXELS = (const jubyte *)GLYPHS[GLYPHCOUNTER].pixels; \
    if (!PIXELS) { \
        NULLGLYPHCODE; \
    } \
    ROWBYTES = GLYPHS[GLYPHCOUNTER].rowBytes; \
    LEFT     = GLYPHS[GLYPHCOUNTER].x; \
    TOP      = GLYPHS[GLYPHCOUNTER].y; \
    WIDTH    = GLYPHS[GLYPHCOUNTER].width; \
    HEIGHT   = GLYPHS[GLYPHCOUNTER].height; \
\
    /* if any clipping required, modify parameters now */ \
    RIGHT  = LEFT + WIDTH; \
    BOTTOM = TOP + HEIGHT; \
    if (LEFT < CLIPLEFT) { \
    /* Multiply needed for LCD text as PIXELS is really BYTES */ \
        PIXELS += (CLIPLEFT - LEFT) * BYTESPERPIXEL ; \
        LEFT = CLIPLEFT; \
    } \
    if (TOP < CLIPTOP) { \
        PIXELS += (CLIPTOP - TOP) * ROWBYTES; \
        TOP = CLIPTOP; \
    } \
    if (RIGHT > CLIPRIGHT) { \
        RIGHT = CLIPRIGHT; \
    } \
    if (BOTTOM > CLIPBOTTOM) { \
        BOTTOM = CLIPBOTTOM; \
    } \
    if (RIGHT