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

0	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

Remarks

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

DPLOT_PLOTMETRICS

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

Page url: http://www.dplot.com/lib/index.htm?dplot_getbitmapex.htm