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Android开机动画，framework修改Bootanimation动画绘制文字。

frameworks/base/cmds/bootanimation/bootanimation.cpp

绘制时间的一个方法

// We render 12 or 24 hour time.
void BootAnimation::drawClock(const Font& font, const int xPos, const int yPos) {static constexpr char TIME_FORMAT_12[] = "%l:%M";static constexpr char TIME_FORMAT_24[] = "%H:%M";static constexpr int TIME_LENGTH = 6;
获取系统时间time_t rawtime;time(&rawtime);struct tm* timeInfo = localtime(&rawtime);char timeBuff[TIME_LENGTH];//显示时间的字符串const char* timeFormat = mTimeFormat12Hour ? TIME_FORMAT_12 : TIME_FORMAT_24;size_t length = strftime(timeBuff, TIME_LENGTH, timeFormat, timeInfo);if (length != TIME_LENGTH - 1) {SLOGE("Couldn't format time; abandoning boot animation clock");mClockEnabled = false;return;}char* out = timeBuff[0] == ' ' ? &timeBuff[1] : &timeBuff[0];int x = xPos;int y = yPos;//绘制文本drawText(out, font, false, &x, &y);
}

绘制文本

void BootAnimation::drawText(const char* str, const Font& font, bool bold, int* x, int* y) {glEnable(GL_BLEND);  // Allow us to draw on top of the animationglBindTexture(GL_TEXTURE_2D, font.texture.name);const int len = strlen(str);const int strWidth = font.char_width * len;if (*x == TEXT_CENTER_VALUE) {*x = (mWidth - strWidth) / 2;} else if (*x < 0) {*x = mWidth + *x - strWidth;}if (*y == TEXT_CENTER_VALUE) {*y = (mHeight - font.char_height) / 2;} else if (*y < 0) {*y = mHeight + *y - font.char_height;}int cropRect[4] = { 0, 0, font.char_width, -font.char_height };for (int i = 0; i < len; i++) {char c = str[i];if (c < FONT_BEGIN_CHAR || c > FONT_END_CHAR) {c = '?';}// Crop the texture to only the pixels in the current glyphconst int charPos = (c - FONT_BEGIN_CHAR);  // Position in the list of valid charactersconst int row = charPos / FONT_NUM_COLS;const int col = charPos % FONT_NUM_COLS;cropRect[0] = col * font.char_width;  // Left of columncropRect[1] = row * font.char_height * 2; // Top of row// Move down to bottom of regular (one char_heigh) or bold (two char_heigh) linecropRect[1] += bold ? 2 * font.char_height : font.char_height;glTexParameteriv(GL_TEXTURE_2D, GL_TEXTURE_CROP_RECT_OES, cropRect);glDrawTexiOES(*x, *y, 0, font.char_width, font.char_height);*x += font.char_width;}glDisable(GL_BLEND);  // Return to the animation's default behaviourglBindTexture(GL_TEXTURE_2D, 0);
}

初始化字体

声明一个成员变量Font。

来到android()的initFont()

这是一个文件名字符串

static const char CLOCK_FONT_ASSET[] = "images/clock_font.png";

opengl只是支持图片纹理，所以文件是一张图片

然后会把这个图片加载进来，设置宽高等等。

绘制

对这个图片进行裁剪

我们新增代码在这里TEXT_CENTER_VALUE居中显示， yc + mAndroid[0].h计算绘制的y坐标系

yc是原本Android动画的一个坐标系，但是我们不能覆盖他，所以要比他高，放到原生Android动画的上边+ mAndroid[0].h

drawClock(mClockFont, TEXT_CENTER_VALUE, yc + mAndroid[0].h);

bool BootAnimation::android()
{SLOGD("%sAnimationShownTiming start time: %" PRId64 "ms", mShuttingDown ? "Shutdown" : "Boot",elapsedRealtime());initTexture(&mAndroid[0], mAssets, "images/android-logo-mask.png");initTexture(&mAndroid[1], mAssets, "images/android-logo-shine.png");mCallbacks->init({});// clear screenglShadeModel(GL_FLAT);//qfh addbool hasInitFont = false;if (initFont(&mClockFont, CLOCK_FONT_ASSET) == NO_ERROR) {hasInitFont = true;ALOGD("android init Font ok ,fontname = %u",mClockFont.texture.name);}//qfh addglDisable(GL_DITHER);glDisable(GL_SCISSOR_TEST);glClearColor(0,0,0,1);glClear(GL_COLOR_BUFFER_BIT);eglSwapBuffers(mDisplay, mSurface);glEnable(GL_TEXTURE_2D);glTexEnvx(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);const GLint xc = (mWidth  - mAndroid[0].w) / 2;const GLint yc = (mHeight - mAndroid[0].h) / 2;// const Rect updateRect(xc, yc, xc + mAndroid[0].w, yc + mAndroid[0].h);//qfh modifyconst Rect updateRect(xc, yc, xc + mAndroid[0].w, yc + mAndroid[0].h*2);glScissor(updateRect.left, mHeight - updateRect.bottom, updateRect.width(),updateRect.height() * 2);//qfh modify// Blend stateglBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);glTexEnvx(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);const nsecs_t startTime = systemTime();do {nsecs_t now = systemTime();double time = now - startTime;float t = 4.0f * float(time / us2ns(16667)) / mAndroid[1].w;GLint offset = (1 - (t - floorf(t))) * mAndroid[1].w;GLint x = xc - offset;glDisable(GL_SCISSOR_TEST);glClear(GL_COLOR_BUFFER_BIT);glEnable(GL_SCISSOR_TEST);glDisable(GL_BLEND);glBindTexture(GL_TEXTURE_2D, mAndroid[1].name);glDrawTexiOES(x,                 yc, 0, mAndroid[1].w, mAndroid[1].h);glDrawTexiOES(x + mAndroid[1].w, yc, 0, mAndroid[1].w, mAndroid[1].h);glEnable(GL_BLEND);glBindTexture(GL_TEXTURE_2D, mAndroid[0].name);glDrawTexiOES(xc, yc, 0, mAndroid[0].w, mAndroid[0].h);drawClock(mClockFont, TEXT_CENTER_VALUE, yc + mAndroid[0].h);EGLBoolean res = eglSwapBuffers(mDisplay, mSurface);if (res == EGL_FALSE)break;// 12fps: don't animate too fast to preserve CPUconst nsecs_t sleepTime = 83333 - ns2us(systemTime() - now);if (sleepTime > 0)usleep(sleepTime);checkExit();} while (!exitPending());glDeleteTextures(1, &mAndroid[0].name);glDeleteTextures(1, &mAndroid[1].name);//qfh addif (hasInitFont)glDeleteTextures(1, &mClockFont.texture.name);//qfh addreturn false;
}

opengl绘制源码分析

安卓原生的开机动画是一个渐变色，由白色到灰色的渐变，直到launcher启动完成。
主要是这两个图片起作用

initTexture就是初始化纹理的意思，这就是aosp原生的动画图片，这个Android字样是镂空的，由其他图片去填充它，

下面这是第二张图片，也加载了

一白一灰，原理就是扫光动画，它在最底层，，两张图片叠加就可以动画了，把这张图片从左往右一直反复移动，就可看到一白一灰的渐变动画了。
看下这个方法做了什么

打开一个文件转换成Bitmap

Asset* asset = assets.open(name, Asset::ACCESS_BUFFER);if (asset == nullptr)return NO_INIT;SkBitmap bitmap;sk_sp<SkData> data = SkData::MakeWithoutCopy(asset->getBuffer(false),asset->getLength());sk_sp<SkImage> image = SkImage::MakeFromEncoded(data);image->asLegacyBitmap(&bitmap, SkImage::kRO_LegacyBitmapMode);asset->close();delete asset;

这两个才是opengl部分。绑定图片纹理图案，

glScissor(updateRect.left, mHeight - updateRect.bottom, updateRect.width(),updateRect.height() * 2);

裁剪区域，不完全绘制屏幕的全部区域，选择性裁剪绘制显示区域。

glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);glTexEnvx(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);

叠加融合，就是两张图片叠加在一起绘制显示，

 do {nsecs_t now = systemTime();double time = now - startTime;float t = 4.0f * float(time / us2ns(16667)) / mAndroid[1].w;GLint offset = (1 - (t - floorf(t))) * mAndroid[1].w;GLint x = xc - offset;glDisable(GL_SCISSOR_TEST);glClear(GL_COLOR_BUFFER_BIT);glEnable(GL_SCISSOR_TEST);glDisable(GL_BLEND);//绑定，绘制mAndroid[1]的图片glBindTexture(GL_TEXTURE_2D, mAndroid[1].name);glDrawTexiOES(x,                 yc, 0, mAndroid[1].w, mAndroid[1].h);glDrawTexiOES(x + mAndroid[1].w, yc, 0, mAndroid[1].w, mAndroid[1].h);//开启融合glEnable(GL_BLEND);//绑定 mAndroid[0]的图片，glBindTexture(GL_TEXTURE_2D, mAndroid[0].name);glDrawTexiOES(xc, yc, 0, mAndroid[0].w, mAndroid[0].h);drawClock(mClockFont, TEXT_CENTER_VALUE, yc + mAndroid[0].h);//调用opengl的方法显示到屏幕上EGLBoolean res = eglSwapBuffers(mDisplay, mSurface);if (res == EGL_FALSE)break;// 12fps: don't animate too fast to preserve CPUconst nsecs_t sleepTime = 83333 - ns2us(systemTime() - now);if (sleepTime > 0)usleep(sleepTime);checkExit();} while (!exitPending());

do,while循环绘制核心，开机动画是不断变化的，所以肯定在这个循环里实现，不断绘制的过程，绘制是有帧率的，循环不会一直执行的，因为会有功耗，所以12fps为一次绘制，一秒绘制12张图片