DataGraphWrapAndOverwrite
A continuous data graph which will fill the graph with elements, and overwrite the first elements with new values after the graph has filled. There will be a gap between the newly inserted element and the element after. This similar behavior to a heart beat monitor.
Inherits from: AbstractDataGraphWithY, AbstractDataGraph, Container, Drawable
Inherited by: GraphWrapAndOverwrite< CAPACITY >
Public Functions
| virtual void | clear() |
| Clears the graph to its blank/initial state. | |
| DataGraphWrapAndOverwrite(int16_t capacity, int * values) | |
| Initializes a new instance of the DataGraphWrapAndOverwrite class. | |
| virtual int32_t | indexToGlobalIndex(int16_t index) const |
| Convert an index to global index. | |
Protected Functions
| virtual int16_t | addValue(int value) |
| Adds a value to the internal data array and keeps track of when graph points, graph axis and the entire graph needs to be redrawn (invalidated). | |
| virtual void | beforeAddValue() |
| This function is called before a new value (data point) is added. | |
Protected Attributes
| int16_t | current |
| The current index (used to keep track of where to insert new data point in value array) | |
Additional inherited members
Public Functions inherited from AbstractDataGraphWithY
| AbstractDataGraphWithY(int16_t capacity, int * values) | |
| Initializes a new instance of the AbstractDataGraphWithY class. | |
| int16_t | addDataPoint(float y) |
| Adds a new data point to the end of the graph. | |
| int16_t | addDataPoint(int y) |
| Adds a new data point to the end of the graph. | |
| virtual int | getGraphRangeXMax() const |
| Gets the maximum x coordinate for the graph. | |
| virtual int | getGraphRangeXMin() const |
| Gets the minimum x coordinate for the graph. | |
| virtual float | getGraphRangeYMaxAsFloat() const |
| Gets maximum y coordinate for the graph. | |
| virtual int | getGraphRangeYMaxAsInt() const |
| Gets maximum y coordinate for the graph. | |
| virtual float | getGraphRangeYMinAsFloat() const |
| Gets minimum y coordinate for the graph. | |
| virtual int | getGraphRangeYMinAsInt() const |
| Gets minimum y coordinate for the graph. | |
| virtual float | getXAxisOffsetAsFloat() const |
| Get x coordinate axis offset value. | |
| virtual int | getXAxisOffsetAsInt() const |
| Get x coordinate axis offset value. | |
| virtual float | getXAxisScaleAsFloat() const |
| Get x coordinate axis scale value. | |
| virtual int | getXAxisScaleAsInt() const |
| Get x coordinate axis scale value. | |
| virtual void | setGraphRangeX(int min, int max) |
| Sets minimum and maximum x coordinates for the graph. | |
| virtual void | setGraphRangeY(float min, float max) |
| Sets minimum and maximum y coordinates for the graph. | |
| virtual void | setGraphRangeY(int min, int max) |
| Sets minimum and maximum y coordinates for the graph. | |
| void | setGraphRangeYAuto(bool showXaxis =true, int margin =0) |
| Automatic adjust min and max y coordinate to show entire graph. | |
| virtual void | setScale(int scale) |
| Sets a scaling factor to be multiplied on each added element. | |
| virtual void | setXAxisOffset(float offset) |
| Set x coordinate axis offset value. | |
| virtual void | setXAxisOffset(int offset) |
| Set x coordinate axis offset value. | |
| virtual void | setXAxisScale(float scale) |
| Set x coordinate axis scale value. | |
| virtual void | setXAxisScale(int scale) |
| Set x coordinate axis scale value. | |
Protected Functions inherited from AbstractDataGraphWithY
| int16_t | addDataPointScaled(int y) |
| Same as addDataPoint(int) except the passed argument is assumed scaled. | |
| virtual int | getGraphRangeYMaxScaled() const |
| Gets maximum y coordinate for the graph. | |
| virtual int | getGraphRangeYMinScaled() const |
| Gets minimum y coordinate for the graph. | |
| virtual int | getXAxisOffsetScaled() const |
| Get x axis offset as a scaled value. | |
| virtual int | getXAxisScaleScaled() const |
| Get x axis scale as a scaled value. | |
| virtual int | indexToDataPointXScaled(int16_t index) const |
| Same as indexToDataPointXAsInt(int16_t) except the returned value is left scaled. | |
| virtual int | indexToDataPointYScaled(int16_t index) const |
| Same as indexToDataPointYAsInt(int16_t) except the returned value is left scaled. | |
| virtual CWRUtil::Q5 | indexToScreenXQ5(int16_t index) const |
| Gets screen x coordinate for a specific data point added to the graph. | |
| virtual CWRUtil::Q5 | indexToScreenYQ5(int16_t index) const |
| Gets screen y coordinate for a specific data point added to the graph. | |
| virtual int16_t | realIndex(int16_t index) const |
| Get the real index in the yValues array of the given index. | |
| virtual void | setGraphRangeYScaled(int min, int max) |
| Same as setGraphRangeY(int,int) except the passed arguments are assumed scaled. | |
| virtual void | setXAxisOffsetScaled(int offset) |
| Set x coordinate axis offset value with a pre-scaled offset value. | |
| virtual void | setXAxisScaleScaled(int scale) |
| Set x coordinate axis scale value using a pre-scaled value. | |
| virtual CWRUtil::Q5 | valueToScreenXQ5(int x) const |
| Gets screen x coordinate for an absolute value. | |
| virtual CWRUtil::Q5 | valueToScreenYQ5(int y) const |
| Gets screen y coordinate for an absolute value. | |
| virtual bool | xScreenRangeToIndexRange(int16_t xLo, int16_t xHi, int16_t & indexLow, int16_t & indexHigh) const |
| Gets index range for screen x coordinate range taking the current graph range into account. | |
Protected Attributes inherited from AbstractDataGraphWithY
| uint32_t | dataCounter |
| The data counter of how many times addDataPoint() has been called. | |
| int | xOffset |
| The x axis offset (real value of data point at index 0) | |
| int | xScale |
| The x axis scale (increment between two data points) | |
| int * | yValues |
| The values of the graph. | |
Public Classes inherited from AbstractDataGraph
| class | GraphClickEvent |
| An object of this type is passed with each callback that is sent when the graph is clicked. | |
| class | GraphDragEvent |
| An object of this type is passed with each callback that is sent when the graph is dragged. | |
Public Functions inherited from AbstractDataGraph
| AbstractDataGraph(int16_t capacity) | |
| Initializes a new instance of the AbstractDataGraph class. | |
| void | addBottomElement(AbstractGraphDecoration & d) |
| Adds an element to be shown in the area below the graph. | |
| void | addGraphElement(AbstractGraphElement & d) |
| Adds a graph element which will display the graph. | |
| void | addLeftElement(AbstractGraphDecoration & d) |
| Adds an element to be shown in the area to the left of the graph. | |
| void | addRightElement(AbstractGraphDecoration & d) |
| Adds an element to be shown in the area to the right of the graph. | |
| void | addTopElement(AbstractGraphDecoration & d) |
| Adds an element to be shown in the area above the graph. | |
| uint8_t | getAlpha() const |
| Gets the current alpha value of the widget. | |
| int16_t | getGapBeforeIndex() const |
| Gets gap before index as set using setGapBeforeIndex(). | |
| int16_t | getGraphAreaHeight() const |
| Gets graph area height. | |
| int16_t | getGraphAreaHeightIncludingPadding() const |
| Gets graph area height including padding (but not margin). | |
| int16_t | getGraphAreaMarginBottom() const |
| Gets graph margin bottom. | |
| int16_t | getGraphAreaMarginLeft() const |
| Gets graph margin left. | |
| int16_t | getGraphAreaMarginRight() const |
| Gets graph margin right. | |
| int16_t | getGraphAreaMarginTop() const |
| Gets graph margin top. | |
| int16_t | getGraphAreaPaddingBottom() const |
| Gets graph area padding bottom. | |
| int16_t | getGraphAreaPaddingLeft() const |
| Gets graph area padding left. | |
| int16_t | getGraphAreaPaddingRight() const |
| Gets graph area padding right. | |
| int16_t | getGraphAreaPaddingTop() const |
| Gets graph area padding top. | |
| int16_t | getGraphAreaWidth() const |
| Gets graph area width. | |
| int16_t | getGraphAreaWidthIncludingPadding() const |
| Gets graph area width including padding (but not margin). | |
| virtual int | getGraphRangeXMax() const =0 |
| Gets the maximum x coordinate for the graph. | |
| virtual int | getGraphRangeXMin() const =0 |
| Gets the minimum x coordinate for the graph. | |
| virtual float | getGraphRangeYMaxAsFloat() const =0 |
| Gets maximum y coordinate for the graph. | |
| virtual int | getGraphRangeYMaxAsInt() const =0 |
| Gets maximum y coordinate for the graph. | |
| virtual float | getGraphRangeYMinAsFloat() const =0 |
| Gets minimum y coordinate for the graph. | |
| virtual int | getGraphRangeYMinAsInt() const =0 |
| Gets minimum y coordinate for the graph. | |
| int16_t | getMaxCapacity() const |
| Gets the capacity (max number of points) of the graph. | |
| virtual bool | getNearestIndexForScreenX(int16_t x, int16_t & index) const |
| Gets graph index nearest to the given screen x coordinate. | |
| virtual bool | getNearestIndexForScreenXY(int16_t x, int16_t y, int16_t & index) |
| Gets graph index nearest to the given screen position. | |
| int | getScale() const |
| Gets the scaling factor previously set using setScale(). | |
| int16_t | getUsedCapacity() const |
| Gets the number of point used by the graph. | |
| virtual void | handleClickEvent(const ClickEvent & evt) |
| Defines the event handler interface for ClickEvents. | |
| virtual void | handleDragEvent(const DragEvent & evt) |
| Defines the event handler interface for DragEvents. | |
| float | indexToDataPointXAsFloat(int16_t index) const |
| Get the data point x value for the given graph point index. | |
| int | indexToDataPointXAsInt(int16_t index) const |
| Get the data point x value for the given graph point index. | |
| float | indexToDataPointYAsFloat(int16_t index) const |
| Get the data point y value for the given graph point index. | |
| int | indexToDataPointYAsInt(int16_t index) const |
| Get the data point y value for the given graph point index. | |
| int16_t | indexToScreenX(int16_t index) const |
| Get the screen x coordinate for the given graph point index. | |
| int16_t | indexToScreenY(int16_t index) const |
| Get the screen y coordinate for the given graph point index. | |
| void | setAlpha(uint8_t newAlpha) |
| Sets the opacity (alpha value). | |
| void | setClickAction(GenericCallback< const AbstractDataGraph &, const GraphClickEvent & > & callback) |
| Sets an action to be executed when the graph is clicked. | |
| void | setDragAction(GenericCallback< const AbstractDataGraph &, const GraphDragEvent & > & callback) |
| Sets an action to be executed when the graph is dragged. | |
| void | setGapBeforeIndex(int16_t index) |
| Makes gap before the specified index. | |
| void | setGraphAreaMargin(int16_t top, int16_t left, int16_t right, int16_t bottom) |
| Sets graph position inside the widget by reserving a margin around the graph. | |
| void | setGraphAreaPadding(int16_t top, int16_t left, int16_t right, int16_t bottom) |
| Adds some padding around the graph that will not be drawn in (apart from dots, boxes etc. | |
| void | setGraphRange(int xMin, int xMax, float yMin, float yMax) |
| Sets minimum and maximum x and y coordinate ranges for the graph. | |
| void | setGraphRange(int xMin, int xMax, int yMin, int yMax) |
| Sets minimum and maximum x and y coordinate ranges for the graph. | |
| virtual void | setGraphRangeX(int min, int max) =0 |
| Sets minimum and maximum x coordinates for the graph. | |
| virtual void | setGraphRangeY(float min, float max) =0 |
| Sets minimum and maximum y coordinates for the graph. | |
| virtual void | setGraphRangeY(int min, int max) =0 |
| Sets minimum and maximum y coordinates for the graph. | |
| virtual void | setHeight(int16_t height) |
| Sets the height of this drawable. | |
| virtual void | setScale(int scale) |
| Sets a scaling factor to be multiplied on each added element. | |
| virtual void | setWidth(int16_t width) |
| Sets the width of this drawable. | |
| int | float2scaled(float f, int scale) |
| Multiply a floating point value with a constant and round the result. | |
| int | int2scaled(int i, int scale) |
| Multiply an integer value with a constant. | |
| float | scaled2float(int i, int scale) |
| Divide a floating point number with a constant. | |
| int | scaled2int(int i, int scale) |
| Divide an integer with a constant and round the result. | |
Protected Functions inherited from AbstractDataGraph
| int | convertToGraphScale(int value, int scale) const |
| Converts a number with one scale to a number that has the same scale as the graph. | |
| int | float2scaled(float f) const |
| Same as float2scaled(float,int) using the graph's scale. | |
| virtual int | getGraphRangeYMaxScaled() const =0 |
| Gets maximum y coordinate for the graph. | |
| virtual int | getGraphRangeYMinScaled() const =0 |
| Gets minimum y coordinate for the graph. | |
| virtual int | getXAxisOffsetScaled() const |
| Get x axis offset as a scaled value. | |
| virtual int | getXAxisScaleScaled() const |
| Get x axis scale as a scaled value. | |
| virtual int | indexToDataPointXScaled(int16_t index) const =0 |
| Same as indexToDataPointXAsInt(int16_t) except the returned value is left scaled. | |
| virtual int | indexToDataPointYScaled(int16_t index) const =0 |
| Same as indexToDataPointYAsInt(int16_t) except the returned value is left scaled. | |
| virtual CWRUtil::Q5 | indexToScreenXQ5(int16_t index) const =0 |
| Gets screen x coordinate for a specific data point added to the graph. | |
| virtual CWRUtil::Q5 | indexToScreenYQ5(int16_t index) const =0 |
| Gets screen y coordinate for a specific data point added to the graph. | |
| int | int2scaled(int i) const |
| Same as int2scaled(int,int) using the graph's scale. | |
| void | invalidateAllXAxisPoints() |
| Invalidate all x axis points. | |
| void | invalidateGraphArea() |
| Invalidate entire graph area (the center of the graph). | |
| void | invalidateGraphPointAt(int16_t index) |
| Invalidate point at a given index. | |
| void | invalidateXAxisPointAt(int16_t index) |
| Invalidate x axis point at the given index. | |
| float | scaled2float(int i) const |
| Same as scaled2float(int,int) using the graph's scale. | |
| int | scaled2int(int i) const |
| Same as scaled2int(int,int) using the graph's scale. | |
| void | setGraphRangeScaled(int xMin, int xMax, int yMin, int yMax) |
| Same as setGraphRange(int,int,int,int) except the passed arguments are assumed scaled. | |
| virtual void | setGraphRangeYScaled(int min, int max) =0 |
| Same as setGraphRangeY(int,int) except the passed arguments are assumed scaled. | |
| void | updateAreasPosition() |
| Updates the position of all elements in all area after a change in size of the graph area and/or label padding. | |
| virtual CWRUtil::Q5 | valueToScreenXQ5(int x) const =0 |
| Gets screen x coordinate for an absolute value. | |
| virtual CWRUtil::Q5 | valueToScreenYQ5(int y) const =0 |
| Gets screen y coordinate for an absolute value. | |
| virtual bool | xScreenRangeToIndexRange(int16_t xLo, int16_t xHi, int16_t & indexLow, int16_t & indexHigh) const =0 |
| Gets index range for screen x coordinate range taking the current graph range into account. | |
Protected Attributes inherited from AbstractDataGraph
| uint8_t | alpha |
| The alpha of the entire graph. | |
| Container | bottomArea |
| The area below the graph. | |
| int16_t | bottomPadding |
| The graph area bottom padding. | |
| GenericCallback< const AbstractDataGraph &, const GraphClickEvent & > * | clickAction |
| The callback to be executed when this Graph is clicked. | |
| int | dataScale |
| The data scale applied to all values. | |
| GenericCallback< const AbstractDataGraph &, const GraphDragEvent & > * | dragAction |
| The callback to be executed when this Graph is dragged. | |
| int16_t | gapBeforeIndex |
| The graph is disconnected (there is a gap) before this element index. | |
| Container | graphArea |
| The graph area (the center area) | |
| Container | leftArea |
| The area to the left of the graph. | |
| int16_t | leftPadding |
| The graph area left padding. | |
| int16_t | maxCapacity |
| Maximum number of points in the graph. | |
| Container | rightArea |
| The area to the right of the graph. | |
| int16_t | rightPadding |
| The graph area right padding. | |
| Container | topArea |
| The area above the graph. | |
| int16_t | topPadding |
| The graph area top padding. | |
| int16_t | usedCapacity |
| The number of used points in the graph. | |
Public Functions inherited from Container
| virtual void | add(Drawable & d) |
| Adds a Drawable instance as child to this Container. | |
| Container() | |
| virtual bool | contains(const Drawable & d) |
| Query if a given Drawable has been added directly to this Container. | |
| virtual void | draw(const Rect & invalidatedArea) const |
| Draw this drawable. | |
| virtual void | forEachChild(GenericCallback< Drawable & > * function) |
| Executes the specified callback function for each child in the Container. | |
| virtual Drawable * | getFirstChild() |
| Obtain a pointer to the first child of this container. | |
| virtual void | getLastChild(int16_t x, int16_t y, Drawable ** last) |
| Gets the last child in the list of children in this Container. | |
| virtual Rect | getSolidRect() const |
| Get (the largest possible) rectangle that is guaranteed to be solid (opaque). | |
| virtual void | insert(Drawable * previous, Drawable & d) |
| Inserts a Drawable after a specific child node. | |
| virtual void | remove(Drawable & d) |
| Removes a Drawable from the container by removing it from the linked list of children. | |
| virtual void | removeAll() |
| Removes all children in the Container by resetting their parent and sibling pointers. | |
| virtual void | unlink() |
| Removes all children by unlinking the first child. | |
Protected Functions inherited from Container
| virtual Rect | getContainedArea() const |
| Gets a rectangle describing the total area covered by the children of this container. | |
| virtual void | moveChildrenRelative(int16_t deltaX, int16_t deltaY) |
| Calls moveRelative on all children. | |
Protected Attributes inherited from Container
| Drawable * | firstChild |
| Pointer to the first child of this container. Subsequent children can be found through firstChild's nextSibling. | |
Public Functions inherited from Drawable
| virtual void | childGeometryChanged() |
| This function can be called on parent nodes to signal that the size or position of one or more of its children has changed. | |
| virtual void | draw(const Rect & invalidatedArea) const =0 |
| Draw this drawable. | |
| Drawable() | |
| Initializes a new instance of the Drawable class. | |
| void | drawToDynamicBitmap(BitmapId id) |
| Render the Drawable object into a dynamic bitmap. | |
| Rect | getAbsoluteRect() const |
| Helper function for obtaining the rectangle this Drawable covers, expressed in absolute coordinates. | |
| virtual Drawable * | getFirstChild() |
| Function for obtaining the first child of this drawable if any. | |
| int16_t | getHeight() const |
| Gets the height of this Drawable. | |
| virtual void | getLastChild(int16_t x, int16_t y, Drawable ** last) =0 |
| Function for obtaining the the last child of this drawable that intersects with the specified point. | |
| Drawable * | getNextSibling() |
| Gets the next sibling node. | |
| Drawable * | getParent() const |
| Returns the parent node. | |
| const Rect & | getRect() const |
| Gets the rectangle this Drawable covers, in coordinates relative to its parent. | |
| virtual Rect | getSolidRect() const =0 |
| Get (the largest possible) rectangle that is guaranteed to be solid (opaque). | |
| virtual Rect | getSolidRectAbsolute() |
| Helper function for obtaining the largest solid rect (as implemented by getSolidRect()) expressed in absolute coordinates. | |
| virtual void | getVisibleRect(Rect & rect) const |
| Function for finding the visible part of this drawable. | |
| int16_t | getWidth() const |
| Gets the width of this Drawable. | |
| int16_t | getX() const |
| Gets the x coordinate of this Drawable, relative to its parent. | |
| int16_t | getY() const |
| Gets the y coordinate of this Drawable, relative to its parent. | |
| virtual void | handleClickEvent(const ClickEvent & evt) |
| Defines the event handler interface for ClickEvents. | |
| virtual void | handleDragEvent(const DragEvent & evt) |
| Defines the event handler interface for DragEvents. | |
| virtual void | handleGestureEvent(const GestureEvent & evt) |
| Defines the event handler interface for GestureEvents. | |
| virtual void | handleTickEvent() |
| Called periodically by the framework if the Drawable instance has subscribed to timer ticks. | |
| virtual void | invalidate() const |
| Tell the framework that this entire Drawable needs to be redrawn. | |
| virtual void | invalidateRect(Rect & invalidatedArea) const |
| Request that a region of this drawable is redrawn. | |
| bool | isTouchable() const |
| Gets whether this Drawable receives touch events or not. | |
| bool | isVisible() const |
| Gets whether this Drawable is visible. | |
| virtual void | moveRelative(int16_t x, int16_t y) |
| Moves the drawable. | |
| virtual void | moveTo(int16_t x, int16_t y) |
| Moves the drawable. | |
| virtual void | setHeight(int16_t height) |
| Sets the height of this drawable. | |
| void | setPosition(const Drawable & drawable) |
| Sets the position of the Drawable to the same as the given Drawable. | |
| void | setPosition(int16_t x, int16_t y, int16_t width, int16_t height) |
| Sets the size and position of this Drawable, relative to its parent. | |
| void | setTouchable(bool touch) |
| Controls whether this Drawable receives touch events or not. | |
| void | setVisible(bool vis) |
| Controls whether this Drawable should be visible. | |
| virtual void | setWidth(int16_t width) |
| Sets the width of this drawable. | |
| void | setWidthHeight(const Bitmap & bitmap) |
| Sets the dimensions (width and height) of the Drawable without changing the x and y coordinates). | |
| void | setWidthHeight(const Drawable & drawable) |
| Sets the dimensions (width and height) of the Drawable without changing the x and y coordinates). | |
| void | setWidthHeight(const Rect & rect) |
| Sets the dimensions (width and height) of the Drawable without changing the x and y coordinates). | |
| void | setWidthHeight(int16_t width, int16_t height) |
| Sets the dimensions (width and height) of the Drawable without changing the x and y coordinates). | |
| virtual void | setX(int16_t x) |
| Sets the x coordinate of this Drawable, relative to its parent. | |
| void | setXY(const Drawable & drawable) |
| Sets the x and y coordinates of this Drawable. | |
| void | setXY(int16_t x, int16_t y) |
| Sets the x and y coordinates of this Drawable, relative to its parent. | |
| virtual void | setY(int16_t y) |
| Sets the y coordinate of this Drawable, relative to its parent. | |
| virtual void | translateRectToAbsolute(Rect & r) const |
| Helper function for converting a region of this Drawable to absolute coordinates. | |
| virtual | ~Drawable() |
| Finalizes an instance of the Drawable class. | |
Protected Attributes inherited from Drawable
| Drawable * | nextSibling |
| Pointer to the next Drawable. | |
| Drawable * | parent |
| Pointer to this drawable's parent. | |
| Rect | rect |
| The coordinates of this Drawable, relative to its parent. | |
| bool | touchable |
| True if this drawable should receive touch events. | |
| bool | visible |
| True if this drawable should be drawn. | |
Public Functions Documentation
clear
| virtual void clear | ( | ) |
Clears the graph to its blank/initial state.
Reimplements: touchgfx::AbstractDataGraph::clear
DataGraphWrapAndOverwrite
| DataGraphWrapAndOverwrite | ( | int16_t | capacity , | ||
| int * | values | ||||
| ) |
Initializes a new instance of the DataGraphWrapAndOverwrite class.
Parameters:
| capacity | The capacity. |
| values | Pointer to memory with room for capacity elements of type T. |
indexToGlobalIndex
| virtual int32_t indexToGlobalIndex | ( | int16_t | index | ) | |
Convert an index to global index.
The index is the index of any data point, The global index is a value that keeps growing whenever a new data point is added the the graph.
Parameters:
| index | Zero-based index of the point. |
Returns:
The global index.
Reimplements: touchgfx::AbstractDataGraph::indexToGlobalIndex
Protected Functions Documentation
addValue
| virtual int16_t addValue | ( | int | value | ) | |
Adds a value to the internal data array and keeps track of when graph points, graph axis and the entire graph needs to be redrawn (invalidated).
Parameters:
| value | The value to add to the array. |
Returns:
The index of the newly added value.
Reimplements: touchgfx::AbstractDataGraphWithY::addValue
beforeAddValue
| virtual void beforeAddValue | ( | ) |
This function is called before a new value (data point) is added.
This allows for invalidation to be calculated based on the global data counter before it is increased as a result of adding the new point.
Reimplements: touchgfx::AbstractDataGraphWithY::beforeAddValue
Protected Attributes Documentation
current
int16_t current
The current index (used to keep track of where to insert new data point in value array)