Android Gallery3d源码学习总结（二）——绘制流程drawThumbnails

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android Gallery3D drawThumbnails

此函数控制相册表格页、相片表格页、时间分类表格页的展示，非常重要。以下以相册表格页为例进行讲解，其他的就举一反三吧。
准备输入参数

final GridDrawables drawables = mDrawables;
final DisplayList displayList = mDisplayList;
final DisplayItem[] displayItems = mDisplayItems;
final int firstBufferedVisibleSlot = mBufferedVisibleRange.begin;
final int lastBufferedVisibleSlot = mBufferedVisibleRange.end;
final int firstVisibleSlot = mVisibleRange.begin;
final int lastVisibleSlot = mVisibleRange.end;
final int selectedSlotIndex = mSelectedSlot;
final int currentFocusSlot = mCurrentFocusSlot;
final int currentScaleSlot = mCurrentScaleSlot;
final DisplayItem[] itemsDrawn = mItemsDrawn;
itemsDrawn[0] = null; // No items drawn yet.
int drawnCounter = 0;
final GridQuad grid = GridDrawables.sGrid;
grid.bindArrays(gl);
int numTexturesQueued = 0;
Context context = view.getContext();

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通过之前的computeVisibleItems()，已得到显示元素列表，显示元素缓冲数组，缓存可见槽位的范围，可见槽位的范围；得到当前选中的槽位索引selectedSlotIndex、当前焦点槽位索引currentFocusSlot和缩放槽位索引currentScaleSlot。
已画元素的缓存数组，绑定表格类材质。selectedSlotIndex、currentFocusSlot、currentScaleSlot在不进行任何操作时都是-1.

遍历缓存可见槽位范围中的每一个槽位

for (int itrSlotIndex = firstBufferedVisibleSlot; itrSlotIndex <= lastBufferedVisibleSlot; ++itrSlotIndex) {
int index = itrSlotIndex;
...
}

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即遍历每个相册，index是相册序号。

为每个相册分别计算“需要绘制“的最开头那张照片的序号

boolean priority = !(index < firstVisibleSlot || index > lastVisibleSlot);
int startSlotIndex = 0;
final int maxDisplayedItemsPerSlot = (index == mCurrentScaleSlot) ? GridLayer.MAX_DISPLAYED_ITEMS_PER_FOCUSED_SLOT
: GridLayer.MAX_DISPLAYED_ITEMS_PER_SLOT;
if (index != mCurrentScaleSlot) {
for (int j = maxDisplayedItemsPerSlot - 1; j >= 0; --j) {
DisplayItem displayItem = displayItems[(index - firstBufferedVisibleSlot) * GridLayer.MAX_ITEMS_PER_SLOT + j];
if (displayItem == null) {
continue;
} else {
Texture texture = displayItem.getThumbnailImage(context, sThumbnailConfig);
if (texture != null && texture.isLoaded() == false) {
startSlotIndex = j;
break;
}
}
}
}

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priority表示当前槽位在[firstVisibleSlot,lastVisibleSlot]范围中，则为高优先级，可见槽位上的自然是最高优先级喽；
maxDisplayedItemsPerSlot表示每个槽位中最多的显示项目，即每个相册封面的最大缩略图数，此处为4；
startSlotIndex是当前帧每个相册中“需要绘制“的最开头那张照片的序号（取值在0-3之间），注意“需要绘制“的最开头那张照片往往不是相册中的第一张照片，帧动画开始时它通常是第四张照片（第四张被依次压在321张照片下面嘛，因此绘制加载材质都要按照第四张向首张的次序），随着动画和材质逐步加载，它慢慢变为第三张、第二张、第一张。

从第四张向第一张加载材质

// Prime the textures in the reverse order.
for (int j = 0; j < maxDisplayedItemsPerSlot; ++j) {
int stackIndex = (index == mCurrentScaleSlot) ? maxDisplayedItemsPerSlot - j - 1 : j;
DisplayItem displayItem = displayItems[(index - firstBufferedVisibleSlot) * GridLayer.MAX_ITEMS_PER_SLOT
+ stackIndex];
if (displayItem == null) {
continue;
} else {
displayItem.mCurrentSlotIndex = index;
if (selectedSlotIndex != Shared.INVALID && (index <= selectedSlotIndex - 2 || index >= selectedSlotIndex + 2)) {
displayItem.clearScreennailImage();
}
Texture texture = displayItem.getThumbnailImage(context, sThumbnailConfig);
if (index == mCurrentScaleSlot && texture != null && !texture.isLoaded()) {
view.prime(texture, true);
view.bind(texture);
} else if (texture != null && !texture.isLoaded() /*&& numTexturesQueued <= 6*/) {
/*boolean isCached = texture.isCached();*/
view.prime(texture, priority);
view.bind(texture);
/*if (priority && isCached && texture.mState != Texture.STATE_ERROR)
++numTexturesQueued;*/
}
}
}

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因为是正序的处理4个元素，插入队头，因此是按照从第四张向第一张的次序加载材质。无用的代码已经注释掉了。

准备一些变量

if (itrSlotIndex == selectedSlotIndex) {
continue;
}
view.prime(drawables.mTexturePlaceholder, true);
Texture placeholder = (state == GridLayer.STATE_GRID_VIEW) ? drawables.mTexturePlaceholder : null;
final boolean pushDown = (state == GridLayer.STATE_GRID_VIEW || state == GridLayer.STATE_FULL_SCREEN) ? false : true;

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加载占位材质，自己找找看是那个图标；如果是相片表格视图，则占位材质使用这个图标，否则占位材质为空；如果是相片表格视图，则长按选中后向上弹起，否则向下陷下去。

调整显示项目和相机的偏移量

for (int j = 0; j < GridLayer.MAX_ITEMS_PER_SLOT; ++j) {
DisplayItem displayItem = displayItems[(index - firstBufferedVisibleSlot) * GridLayer.MAX_ITEMS_PER_SLOT + j];
if (displayItem == null)
continue;
Texture texture = displayItem.getThumbnailImage(context, sThumbnailConfig);
if (texture == null || !texture.isLoaded()) {
if (currentScaleSlot != index) {
if (j == 0) {
final MediaSet parentSet = displayItem.mItemRef.mParentMediaSet;
if (parentSet != null && parentSet.getNumItems() <= 1) {
displayList.setAlive(displayItem, false);
}
} else {
displayList.setAlive(displayItem, false);
}
}
}
final float dx1 = mScaleGestureDetector.getTopFingerDeltaX();
final float dy1 = mScaleGestureDetector.getTopFingerDeltaY();
final float dx2 = mScaleGestureDetector.getBottomFingerDeltaX();
final float dy2 = mScaleGestureDetector.getBottomFingerDeltaY();
final float span = mScaleGestureDetector.getCurrentSpan();
if (state == GridLayer.STATE_FULL_SCREEN) {
displayList.setOffset(displayItem, false, true, span, dx1, dy1, dx2, dy2);
} else {
if (!mHoldPosition) {
if (state != GridLayer.STATE_GRID_VIEW) {
if (currentScaleSlot == index) {
displayList.setOffset(displayItem, true, false, span, dx1, dy1, dx2, dy2);
} else if (currentScaleSlot != Shared.INVALID) {
displayList.setOffset(displayItem, true, true, span, dx1, dy1, dx2, dy2);
} else {
displayList.setOffset(displayItem, false, false, span, dx1, dy1, dx2, dy2);
}
} else {
float minVal = -1.0f;
float maxVal = GridCamera.EYE_Z * 0.5f;
float zVal = minVal + mSpreadValue;
zVal = FloatUtils.clamp(zVal, minVal, maxVal);
if (Float.isInfinite(zVal) || Float.isNaN(zVal)) {
mCamera.moveZTo(0);
} else {
mCamera.moveZTo(-zVal);
}
}
}
}
}

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第一部分每太看懂，第二部分是得到多点触碰的输入信息，第三部分根据视图调整了照片偏移量和相机距离。

绘制缩略图显示项目

for (int j = startSlotIndex; j < GridLayer.MAX_ITEMS_PER_SLOT; ++j) {
DisplayItem displayItem = displayItems[(index - firstBufferedVisibleSlot) * GridLayer.MAX_ITEMS_PER_SLOT + j];
if (displayItem == null) {
break;
} else {
if (currentFocusSlot == index) {
displayList.setHasFocus(displayItem, true, pushDown);
mTargetFocusMixRatio = 1.0f;
} else {
displayList.setHasFocus(displayItem, false, pushDown);
}
if (j >= maxDisplayedItemsPerSlot)
continue;
Texture texture = displayItem.getThumbnailImage(view.getContext(), sThumbnailConfig);
if (texture != null) {
if (index == mCurrentScaleSlot)
displayItem.mAlive = true;
if ((!displayItem.isAnimating() || !texture.isLoaded())
&& displayItem.getStackIndex() > GridLayer.MAX_ITEMS_PER_SLOT) {
displayList.setAlive(displayItem, true);
continue;
}
if (index < firstVisibleSlot || index > lastVisibleSlot) {
if (view.bind(texture)) {
displayList.setAlive(displayItem, true);
}
continue;
}
drawDisplayItem(view, gl, displayItem, texture, PASS_THUMBNAIL_CONTENT, placeholder,
displayItem.mAnimatedPlaceholderFade);
} else {
// Move on to the next stack.
break;
}
if (drawnCounter >= GridLayer.MAX_ITEMS_DRAWABLE - 1 || drawnCounter < 0) {
break;
}
// Insert in order of z.
itemsDrawn[drawnCounter++] = displayItem;
itemsDrawn[drawnCounter] = null;
}
}

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如果是当前选中，则根据当前视图选择下陷还是弹起；绘制缩略图（其中的displayList.setAlive还没有看懂有什么用）；记录已绘制的items。

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Android Gallery3D源码学习总结（三）—— ... | Android Gallery 3D 特效精华

2011-12-29 11:02
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