frameworks\base\packages\SystemUI\res\layout\quick_settings_brightness_dialog.xml

进度条控件

frameworks\base\packages\SystemUI\src\com\android\systemui\settings\brightness\BrightnessSliderView.java

// Inflated from quick_settings_brightness_dialog
    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        setLayerType(LAYER_TYPE_HARDWARE, null);

        mSlider = requireViewById(R.id.slider);
        mSlider.setAccessibilityLabel(getContentDescription().toString());

        // Finds the progress drawable. Assumes brightness_progress_drawable.xml
        try {
            LayerDrawable progress = (LayerDrawable) mSlider.getProgressDrawable();
            DrawableWrapper progressSlider = (DrawableWrapper) progress
                    .findDrawableByLayerId(android.R.id.progress);
            LayerDrawable actualProgressSlider = (LayerDrawable) progressSlider.getDrawable();
            mProgressDrawable = actualProgressSlider.findDrawableByLayerId(R.id.slider_foreground);
        } catch (Exception e) {
            // Nothing to do, mProgressDrawable will be null.
        }
    }

frameworks\base\packages\SystemUI\src\com\android\systemui\settings\brightness\BrightnessController.java

private volatile boolean mAutomatic;  // Brightness adjusted automatically using ambient light.
    private volatile boolean mIsVrModeEnabled;
    private boolean mListening;
    private boolean mExternalChange;
    private boolean mControlValueInitialized;
    private float mBrightnessMin = PowerManager.BRIGHTNESS_MIN;
    private float mBrightnessMax = PowerManager.BRIGHTNESS_MAX;

    private void updateSlider(float brightnessValue, boolean inVrMode) {
        final float min;
        final float max;
        if (inVrMode) {
            min = mMinimumBacklightForVr;
            max = mMaximumBacklightForVr;
        } else {
            min = mBrightnessMin;
            max = mBrightnessMax;
        }

        // Ensure the slider is in a fixed position first, then check if we should animate.
        if (mSliderAnimator != null && mSliderAnimator.isStarted()) {
            mSliderAnimator.cancel();
        }
        // convertGammaToLinearFloat returns 0-1
        if (BrightnessSynchronizer.floatEquals(brightnessValue,
                convertGammaToLinearFloat(mControl.getValue(), min, max))) {
            // If the value in the slider is equal to the value on the current brightness
            // then the slider does not need to animate, since the brightness will not change.
            return;
        }
        // Returns GAMMA_SPACE_MIN - GAMMA_SPACE_MAX
        final int sliderVal = convertLinearToGammaFloat(brightnessValue, min, max);
        animateSliderTo(sliderVal);
    }

亮度最小值由PowerManager.BRIGHTNESS_MIN控制

frameworks\base\core\java\android\os\PowerManager.java 修改即可

    //Brightness values for new float implementation:
    /**
     * Brightness value for fully on as float.
     * @hide
     */
    public static final float BRIGHTNESS_MAX = 1.0f;

    /**
     * Brightness value for minimum valid brightness as float.
     * @hide
     */
    public static final float BRIGHTNESS_MIN = 0.5f;

    /**
     * Brightness value for fully off in float.
     * @hide
     */
    public static final float BRIGHTNESS_OFF_FLOAT = -1.0f;