一、前言
在本篇之前，很多博客已经实现过图片文本化，但是由于渲染方式的不合理，大部分设计都做不到尽可能实时播放，本篇将在已有的基础上进行一些优化，使得视频文字化具备一定的实时性。
下图总体上视频和文字化的画面基本是实时的，上面是SurfaceView，下面是我们自定义的View类，通过实时抓帧然后实时转bitmap，做到了基本同步。
二、现状
目前很多流行的方式是修改像素的色值，这个性能差距太大，导致卡顿非常严重，无法做到实时性。当然也有通过open gl mask实现的，但是在贴图这一块我们知道，open gl只支持绘制三角、点和线，因此"文字"纹理生成还得利用Canvas实现。
但对于对帧率要求不高的需求，是不是有更好的方案呢？
三、优化方案
优化点1: 使用Shader
网上很多博客都是利用Bitmap#getPixel和Bitmap#setPixel进行，这个计算量显然太大了，就算使用open gl 也未必好，因此首先解决的问题就是使用Shader着色。
优化点2: 提前计算好单个文字所占的最大空间
显然这个原因是更加整齐的排列文字，其次也可以做到降低计算量和提高灵活度
优化点3:使用队列
对于了编解码的开发而言，使用队列不仅可以复用buffer，而且还能提高绘制性能，另外必要时可以丢帧。
基于以上三点，基本可以做到实时字符化画面，当然，我们这里是彩色的，对于灰度图的需求，可通过设置Paint的ColorMatrix实现，总之，要避免遍历修改像素了RGB。
四、关键代码
使用shader着色
ini
this.bitmapShader = new BitmapShader(inputBitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
this.mCharPaint.setShader(bitmapShader);
//用下面方式清空bitmap
boardBitmap.bitmap.eraseColor(Color.TRANSPARENT);计算字符size
ini
private Rect computeMaxCharWidth(TextPaint drawerPaint, String text) {
if (TextUtils.isEmpty(text)) {
return null;
}
Rect result = new Rect(); // 文字所在区域的矩形
Rect md = new Rect();
for (int i = 0; i < text.length(); i++) {
String s = text.charAt(i) + "";
if(TextUtils.isEmpty(s)) {
continue;
}
drawerPaint.getTextBounds(s, 0, 1, md);
if (md.width() > result.width()) {
result.right = md.width();
}
if (md.height() > result.height()) {
result.bottom = md.height();
}
}
return result;
}定义双队列，实现控制和享元机制
arduino
private BitmapPool bitmapPool = new BitmapPool();
private BitmapPool recyclePool = new BitmapPool();
static class BitmapPool {
int width;
int height;
private LinkedBlockingQueue<BitmapItem> linkedBlockingQueue = new LinkedBlockingQueue<>(5);
}
static class BitmapItem{
Bitmap bitmap;
boolean isUsed = false;
}完整代码
ini
public class WordBitmapView extends View {
private final DisplayMetrics mDM;
private TextPaint mCharPaint;
private TextPaint mDrawerPaint = null;
private Bitmap inputBitmap;
private Rect charMxWidth = null ;
private String text = "a1b2c3d4e5f6h7j8k9l0";
private float textBaseline;
private BitmapShader bitmapShader;
public WordBitmapView(Context context) {
this(context, null);
}
public WordBitmapView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public WordBitmapView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
mDM = getResources().getDisplayMetrics();
initPaint();
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
if (widthMode != MeasureSpec.EXACTLY) {
widthSize = mDM.widthPixels / 2;
}
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
if (heightMode != MeasureSpec.EXACTLY) {
heightSize = widthSize / 2;
}
setMeasuredDimension(widthSize, heightSize);
textBaseline = getTextPaintBaseline(mDrawerPaint);
}
public float dp2px(float dp) {
return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, mDM);
}
public float sp2px(float dp) {
return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, dp, mDM);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
recyclePool.clear();
bitmapPool.clear();
}
Matrix matrix = new Matrix();
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
int width = getWidth();
int height = getHeight();
if (width <= 1 || height <= 1) {
return;
}
BitmapItem bitmapItem = bitmapPool.linkedBlockingQueue.poll();
if (bitmapItem == null || inputBitmap == null) {
return;
}
if(!bitmapItem.isUsed){
return;
}
canvas.drawBitmap(bitmapItem.bitmap,matrix,mDrawerPaint);
bitmapItem.isUsed = false;
try {
recyclePool.linkedBlockingQueue.offer(bitmapItem,16,TimeUnit.MILLISECONDS);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public static float getTextPaintBaseline(Paint p) {
Paint.FontMetrics fontMetrics = p.getFontMetrics();
return (fontMetrics.descent - fontMetrics.ascent) / 2 - fontMetrics.descent;
}
private Rect computeMaxCharWidth(TextPaint drawerPaint, String text) {
if (TextUtils.isEmpty(text)) {
return null;
}
Rect result = new Rect(); // 文字所在区域的矩形
Rect md = new Rect();
for (int i = 0; i < text.length(); i++) {
String s = text.charAt(i) + "";
if(TextUtils.isEmpty(s)) {
continue;
}
drawerPaint.getTextBounds(s, 0, 1, md);
if (md.width() > result.width()) {
result.right = md.width();
}
if (md.height() > result.height()) {
result.bottom = md.height();
}
}
return result;
}
private BitmapPool bitmapPool = new BitmapPool();
private BitmapPool recyclePool = new BitmapPool();
static class BitmapPool {
int width;
int height;
private LinkedBlockingQueue<BitmapItem> linkedBlockingQueue = new LinkedBlockingQueue<>(5);
public void clear(){
Iterator<BitmapItem> iterator = linkedBlockingQueue.iterator();
do{
if(!iterator.hasNext()) break;
BitmapItem next = iterator.next();
if(!next.bitmap.isRecycled()) {
next.bitmap.recycle();
}
iterator.remove();
}while (true);
}
public int getWidth() {
return width;
}
public int getHeight() {
return height;
}
public void setHeight(int height) {
this.height = height;
}
public void setWidth(int width) {
this.width = width;
}
}
class BitmapItem{
Bitmap bitmap;
boolean isUsed = false;
}
//视频图片入队
public void queueInputBitmap(Bitmap inputBitmap) {
this.inputBitmap = inputBitmap;
if(charMxWidth == null){
charMxWidth = computeMaxCharWidth(mDrawerPaint,text);
}
if(charMxWidth == null || charMxWidth.width() == 0){
return;
}
if(this.bitmapPool != null && this.inputBitmap != null){
if(this.bitmapPool.getWidth() != this.inputBitmap.getWidth()){
bitmapPool.clear();
recyclePool.clear();
}else if(this.bitmapPool.getHeight() != this.inputBitmap.getHeight()){
bitmapPool.clear();
recyclePool.clear();
}
}
bitmapPool.setWidth(inputBitmap.getWidth());
bitmapPool.setHeight(inputBitmap.getHeight());
recyclePool.setWidth(inputBitmap.getWidth());
recyclePool.setHeight(inputBitmap.getHeight());
BitmapItem boardBitmap = recyclePool.linkedBlockingQueue.poll();
if (boardBitmap == null && inputBitmap != null) {
boardBitmap = new BitmapItem();
boardBitmap.bitmap = Bitmap.createBitmap(inputBitmap.getWidth(), inputBitmap.getHeight(), Bitmap.Config.ARGB_8888);
}
boardBitmap.isUsed = true;
int bitmapWidth = inputBitmap.getWidth();
int bitmapHeight = inputBitmap.getHeight();
int unitWidth = (int) (charMxWidth.width() *1.5);
int unitHeight = charMxWidth.height() + 2;
int centerY = charMxWidth.centerY();
float hLineCharNum = bitmapWidth * 1F / unitWidth;
float vLineCharNum = bitmapHeight * 1F / unitHeight;
this.bitmapShader = new BitmapShader(inputBitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
this.mCharPaint.setShader(bitmapShader);
boardBitmap.bitmap.eraseColor(Color.TRANSPARENT);
Canvas drawCanvas = new Canvas(boardBitmap.bitmap);
int k = (int) (Math.random() * text.length());
for (int i = 0; i < vLineCharNum; i++) {
for (int j = 0; j < hLineCharNum; j++) {
int length = text.length();
int x = unitWidth * j;
int y = centerY + i * unitHeight;
String c = text.charAt(k % length) + "";
drawCanvas.drawText(c, x, y + textBaseline, mCharPaint);
k++;
}
}
try {
bitmapPool.linkedBlockingQueue.offer(boardBitmap,16, TimeUnit.MILLISECONDS);
} catch (InterruptedException e) {
e.printStackTrace();
}
postInvalidate();
}
private void initPaint() {
// 实例化画笔并打开抗锯齿
mCharPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
mCharPaint.setAntiAlias(true);
mCharPaint.setStyle(Paint.Style.FILL);
mCharPaint.setStrokeCap(Paint.Cap.ROUND);
mDrawerPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
mDrawerPaint.setAntiAlias(true);
mDrawerPaint.setStyle(Paint.Style.FILL);
mDrawerPaint.setStrokeCap(Paint.Cap.ROUND);
}
}五、总结
Android中Shader是非常重要的工具，我们无需单独修改像素的情况下就能实现快速渲染字符，得意与Shader出色的渲染能力。另外由于时间原因，这里对字符的绘制并没有做到很精确，仅仅选了一些比较中规中列的排列，后续再继续完善吧。