DPlot_GetBitmapEx function

HBITMAP DPlot_GetBitmapEx(int DocNum, int cx, int cy, DPLOT_PLOTMETRICS *DPM);

Parameters

DocNum	Document index for the document that you want a bitmap picture of (1-32). In practice this will generally (though not necessarily) be the return value of a call to DPlot_Plot.
cx, cy	Requested width and height of the bitmap, in pixels.
*DPM	Address of a DPLOT_PLOTMETRICS structure (see below). The size member of this structure should be set by the caller prior to calling this function. If *DPM is set to NULL, this information is not returned and this function is identical to DPlot_GetBitmap.

Return Values

Generic error attempting to communicate with DPlot. This most often indicates that DPlot is currently busy, e.g. a modal dialog box is open.

<>0

Handle to a device-dependent bitmap. This picture may be drawn in your application with the Windows API functions BitBlt and/or StretchBlt or, with an SS_BITMAP-style frame, with an STM_SETIMAGE message. Although these functions can also work in .NET applications, it is much easier to convert the Win32 bitmap handle to a GDI bitmap and use .NET's features:

Bitmap myBmp;

hbmp = dplot.DPlot_GetBitmapEx(DocNum, cx, cy, ref DPM);

myBmp = Bitmap.FromHbitmap(hbmp);

DeleteObject(hbmp);

pictureBox1.Image = myBmp;

Remarks

Palette information is not returned, so this function does not work particularly well with 256 (or fewer) color displays.

Example usage in demo programs:

Visual Basic 6:	\btest\btest2
Visual C 5/6:	\c\msvc\ctest2
Visual Basic .NET:	\vbnet\Project2.NET
Visual C#:	\csharp\test2

DPLOT_PLOTMETRICS

There are 2 versions of this structure available in DPLOTLIB.DLL version 2.1.0.6 and later. The newer version uses double-precision (8 byte) floating point values, and data is passed from DPlot to DPLOTLIB.DLL in its native format. Using the old version of the structure, data is passed as character strings to DPLOTLIB.DLL and translated there to single-precision (4 byte) floating point. In general the old format is sufficient for most needs. However, if you use a date and time scale on the X axis, or if your data otherwise consists of large numbers with a relatively small difference between the low and high values, the new version should be used. To ensure that the end user has the needed version of DPlot or DPlot Jr, your application should call DPlot_MinVersion(2,1,4,0).

Example programs distributed with DPLOTLIB.DLL and DPlot Jr all use the new version of this structure.

New Version, requires DPLOTLIB.DLL version 2.1.0.6 or later, and DPlot or DPlot Junior version 2.1.4 or later.

In C:

typedef struct tagDPLOT_PLOTMETRICS

{

DWORD size; // size of this structure; should be set by the caller

int hll; // horizontal and

int vll; // vertical coordinates of the lower left corner of

// the plot, in pixels

int hur; // horizontal and

int vur; // vertical coordinates of the upper right corner of

// the plot, in pixels

int dummy; // not used; only for member alignment

double xlo; // value of X at the left plot extent

double ylo; // value of Y at the bottom plot extent

double xhi; // value of X at the right plot extent

double yhi; // value of Y at the top plot extent

double stretch[3]; // scale factors for X, Y, and Z w/ 3D plots

double scale; // scale factor for projection of 3D points

double azimuth; // view angles for 3D views, radians

double elevation;

double ylo2; // Y extents of 2nd Y axis, if any

double yhi2;

} DPLOT_PLOTMETRICS

In Visual Basic:

Type DPLOT_PLOTMETRICS

size As Long ' size of this structure

hll As Long ' horizontal and

vll As Long ' vertical coordinates of the lower left corner of

' the plot, in pixels

hur As Long ' horizontal and

vur As Long ' vertical coordinates of the upper right corner of

' the plot, in pixels

dummy As Long ' not used; only for member alignment

xlo As Double ' value of X at the left plot extent

ylo As Double ' value of Y at the bottom plot extent

xhi As Double ' value of X at the right plot extent

yhi As Double ' value of Y at the top plot extent

stretch(3) As Double ' scale factors for X, Y, and Z w/ 3D plots

scale As Double ' scale factor for projection of 3D points

azimuth As Double ' view angles for 3D views, radians

elevation As Double

ylo2 As Double ' Y extents of 2nd Y axis, if any

yhi2 As Double

End Type

Old Version. Works with any version of DPLOTLIB.DLL and DPlot or DPlot Jr.

In C:

typedef struct tagDPLOT_PLOTMETRICS

{

DWORD size; // size of this structure; should be set by the caller

int hll; // horizontal and

int vll; // vertical coordinates of the lower left corner of

// the plot, in pixels

int hur; // horizontal and

int vur; // vertical coordinates of the upper right corner of

// the plot, in pixels

float xlo; // value of X at the left plot extent

float ylo; // value of Y at the bottom plot extent

float xhi; // value of X at the right plot extent

float yhi; // value of Y at the top plot extent

float stretch[3]; // scale factors for X, Y, and Z w/ 3D plots

float scale; // scale factor for projection of 3D points

float azimuth; // view angles for 3D views, radians

float elevation;

float ylo2; // Y extents of 2nd Y axis, if any

float yhi2;

} DPLOT_PLOTMETRICS

In Visual Basic:

Type DPLOT_PLOTMETRICS

size As Long ' size of this structure

hll As Long ' horizontal and

vll As Long ' vertical coordinates of the lower left corner of

' the plot, in pixels

hur As Long ' horizontal and

vur As Long ' vertical coordinates of the upper right corner of

' the plot, in pixels

xlo As Single ' value of X at the left plot extent

ylo As Single ' value of Y at the bottom plot extent

xhi As Single ' value of X at the right plot extent

yhi As Single ' value of Y at the top plot extent

stretch(3) As Single ' scale factors for X, Y, and Z w/ 3D plots

scale As Single ' scale factor for projection of 3D points

azimuth As Single ' view angles for 3D views, radians

elevation As Single

ylo2 As Single ' Y extents of 2nd Y axis, if any

yhi2 As Single

End Type

Using DPLOT_PLOTMETRICS

The information returned in this structure can be used to translate pixel coordinates (mouse position, for example) into X,Y coordinates in data space. The btest2 Visual Basic and ctest2 C demos illustrate this functionality for linear scales. Translating pixels to X and Y for various scaling types is described below in Visual Basic terminology. In all cases, x and y are the pixel coordinates of interest (0,0 is at the upper left corner of the bitmap), wx and wy are the translated X and Y values; DPM is the DPLOT_PLOTMETRICS structure returned by DPlot_GetBitmapEx. Reverse scaling probability plots is outside the scope of this documentation.

Linear X:

wx = DPM.xlo + (x - DPM.hll) * (DPM.xhi - DPM.xlo) /(DPM.hur - DPM.hll)

Linear Y:

wy = DPM.ylo + (y - DPM.vll) * (DPM.yhi - DPM.ylo) / (DPM.vur - DPM.vll)

Logarithmic X:

wx = DPM.xlo * (DPM.xhi/DPM.xlo) ^ ( (x-DPM.hll)/(DPM.hur-DPM.hll) )

Logarithmic Y:

wy = DPM.ylo * (DPM.yhi/DPM.ylo) ^ ( (y-DPM.vll)/(DPM.vur-DPM.vll) )

Polar coordinates:

xp = ( x - ( DPM.hll +DPM.hur )/2. ) * 2.0 * _

( DPM.yhi - DPM.ylo ) / ( DPM.hur - DPM.hll ) + DPM.ylo

yp = ( y - ( DPM.vll +DPM.vur )/2. ) * 2.0 * _

( DPM.yhi - DPM.ylo ) / ( DPM.vur - DPM.vll ) + DPM.ylo

If xp = 0 Then

If yp < 0 Then

alpha = -90

Else

alpha = 90

End If

Elseif xp < 0 then

alpha = atn(yp/xp) * 180. / PI - 180.

Else

alpha = atn(yp/xp) * 180. / PI

End If

If alpha < 0. Then

alpha = 360 + alpha

End If

radius = sqr(xp^2 + yp^2)

Triangle plot:

wy = 100 * (DPM.vll-y) / (DPM.vll-DPM.vur)

wx = 100 * ( (x-DPM.hll) - 0.01*wy*(DPM.vll-DPM.vur)*0.5773502691896) / _

(DPM.hur-DPM.hll)

N185 Hydraulic scale:

wx = ( (x - DPM.hll) * (DPM.xhi^1.85 - DPM.xlo^1.85) / _

(DPM.hur-DPM.hll) + DPM.xlo^1.85 )^(1.0/1.85)

Getting pixel values for projected 3D points

This procedure might be useful if you want to draw your own symbols or other graphics on a bitmap of a 3D projection returned by DPlot. The following example is in Visual Basic:

Dim DPM As DPLOT_PLOTMETRICS

Dim ct(3) As Double

Dim st(3) As Double

Private Sub AngleTransforms()

Dim roll As Double

Dim yaw As Double

If (DPM.azimuth = PI / 2) Then

ct(2) = 0

st(2) = 1

ElseIf (DPM.azimuth = 3 * PI / 2) Then

ct(2) = 0

st(2) = -1

Else

ct(2) = Cos(DPM.azimuth)

st(2) = Sin(DPM.azimuth)

End If

roll = DPM.elevation * st(2)

yaw = 1.5 * PI + DPM.elevation * ct(2)

' Find angles from midpoint to viewpoint:

ct(0) = Cos(yaw)

st(0) = Sin(yaw)

ct(1) = Cos(roll)

st(1) = Sin(roll)

' Force roll angle to keep vertical lines vertical

If (ct(2) <> 0 And st(0) <> 0) Then

st(1) = -st(2) * ct(0) / (ct(2) * st(0))

If (Abs(st(1)) >= 1) Then

If (st(1) < 0) Then

st(1) = -1

Else

st(1) = 1

End If

Else

ct(1) = Sqr(1 - st(1) * st(1))

End If

End Sub

Private Sub Transform3D(Xin As Double, Yin As Double, Zin As Double, pt As POINTAPI)

Dim X, Y, Z As Double

Dim xa, xb, ya, yb, za, zb As Double

Dim h As Double ' Horizontal projection

Dim v As Double ' Vertical projection

Dim d As Double ' Depth into screen

' "stretch" coordinates. These values correspond to the X, Y, and Z scale factors

' on DPlot's Contour Options dialog.

X = Xin * DPM.stretch(0)

Y = Yin * DPM.stretch(1)

Z = Zin * DPM.stretch(2)

' 3D to 2D transformation

' yaw

xa = ct(0) * X - st(0) * Z

ya = Y

za = st(0) * X + ct(0) * Z

' roll

xb = ct(1) * xa + st(1) * ya

yb = ct(1) * ya - st(1) * xa

zb = za

' azimuth

h = -ct(2) * yb - st(2) * zb

v = xb

d = ct(2) * zb - st(2) * yb

' Now scale h and v to the output:

pt.X = DPM.hll + DPM.scale * (h - DPM.xlo)

pt.Y = DPM.vur + DPM.scale * (DPM.yhi - v)

End Sub

Private Sub DoStuff()

Dim X As Double

Dim Y As Double

Dim Z As Double

Dim pt As POINTAPI

PI = 4# * Atn(1#)

' Get a bitmap using DPlot_GetBitmapEx

Call AngleTransforms

' Get X, Y, Z from text boxes, whatever...

Call Transform3D(X, Y, Z, pt)

End Sub

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