Apidemo学习 WindowSurface

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                    if (!mActive) {//绘制开始 处于活动状态                        mActive = true;                        notify();                    }                                        // Lock the canvas for drawing.                     //拿到 surface的 canvas ,开始绘制这个canvas                    Canvas canvas = mSurfaceHolder.lockCanvas();                    if (canvas == null) {                        Log.i("WindowSurface", "Failure locking canvas");                        continue;                    }                                        // Update graphics.                    if (!mInitialized) {                        mInitialized = true;                        mPoint1.init(canvas.getWidth(), canvas.getHeight(), mMinStep);                        mPoint2.init(canvas.getWidth(), canvas.getHeight(), mMinStep);                        mColor.init(127, 127, 1);                    } else {                        mPoint1.step(canvas.getWidth(), canvas.getHeight(),                                mMinStep, mMaxStep);                        mPoint2.step(canvas.getWidth(), canvas.getHeight(),                                mMinStep, mMaxStep);                        mColor.step(127, 127, 1, 3);                    }                    mBrightLine+=2;                    if (mBrightLine > (NUM_OLD*2)) {                        mBrightLine = -2;                    }                                        // Clear background. 绘制背景 也是清空                    canvas.drawColor(mBackground.getColor());                                        // Draw old lines.绘制旧的线条                    for (int i=mNumOld-1; i>=0; i--) {                        mForeground.setColor(mOldColor[i] | makeGreen(i)); //开始绿色的传递                        mForeground.setAlpha(((NUM_OLD-i) * 255) / NUM_OLD);                        int p = i*4;                        canvas.drawLine(mOld[p], mOld[p+1], mOld[p+2], mOld[p+3], mForeground);                    }                                        // Draw new line.                    int red = (int)mColor.x + 128;                    if (red > 255) red = 255;                    int blue = (int)mColor.y + 128;                    if (blue > 255) blue = 255;                    int color = 0xff000000 | (red<<16) | blue;//这里可能是设置红色的?                    mForeground.setColor(color | makeGreen(-2));//新的线条                    canvas.drawLine(mPoint1.x, mPoint1.y, mPoint2.x, mPoint2.y, mForeground);                                        // Add in the new line.                    if (mNumOld > 1) {                        System.arraycopy(mOld, 0, mOld, 4, (mNumOld-1)*4);                        System.arraycopy(mOldColor, 0, mOldColor, 1, mNumOld-1);                    }                    if (mNumOld < NUM_OLD) mNumOld++;                    mOld[0] = mPoint1.x;                    mOld[1] = mPoint1.y;                    mOld[2] = mPoint2.x;                    mOld[3] = mPoint2.y;                    mOldColor[0] = color;                                        // All done!完成 ,然后 是否canvas 显示在屏幕                    mSurfaceHolder.unlockCanvasAndPost(canvas);                 }            }        }    }}
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