yang686526

entities and colors
entities and colors
hello again,
i'm using the following code in order to set the color of a line (dd111.01):
code:
oduint8 red = 255;
oduint8 green = 255;
oduint8 blue = 255;
odcmcolor cmcolor;
cmcolor.setrgb(red, green, blue);
pline->setcolor(cmcolor);
when i open the corresponding file in autocad the line color is "white" (index color 7). this color looks white when background is black and black when background is white.
but if in the same code i set the red, green and blue values to 0, then the line color in autocad is "color 18", an "almost black" color that is visible with white background but almost invisible with black background.
wouldn't be logical that in this latter case the line color in autocad were "white" color too?.
also related is the fact that using dd109, function odcmlookupaci(rgb(0,0,0)) returns 7.
maybe this is not a very important question but i'd like to know the reason for this.
thanks a lot for all your help.
the color can be specified (for cmcolor or for an entity) by index or by rgb. if you want to use some specific rgb value - use rgb methods. if you want to use for example 7 color visible on any background, use setcolorindex(7).
but note that rgb colors can be stored only in ac2004 and later file versions. while saving to minor versions only index is used (look up for nearest color index is performed if the color was specified by rgb).
sergey slezkin
thanks, i understood it.
hello again,
i've got another question:
if i use rgb method to set the entity color like in first post, with red, green and blue values set to 255, when the application writes the dwg file and i open it in autocad, the color is white/black, as expected.
but if in my application i change the background color to white (like in odamfcapp):
ccolordialog dlg;
dlg.m_cc.flags |= cc_fullopen | cc_rgbinit;
dlg.m_cc.rgbresult =theapp.activebackground();
if (idok == dlg.domodal())
{
colorref color = dlg.getcolor();
theapp.setactivebackground(color);
}
then the entity is not visible, as if its color were just white.
if i use setcolorindex(7), it works fine but i'd like to use rgb values and i'd like to let users change the background.
edit: i've also tried with m_pdevice->setbackgroundcolor(color)
last edited by suaser; 8th september 2004 at 03:07 amfff">.

you are absolutely correct... entity with color, specified by rgb, can become invisible when background color is specified by rgb too (in case equal rgbs). this can't be avoided. imho the single possible advice here - you can use your own palette, and change it when background color changes, to make all its colors visible... but in this case you shouldn't use rgb colors for entities...
sincerely yours,
george udov
if you specify color by rgb(255,255,255) that means white not white/black and such entity is invisible on white background in ac2004 and ac2005. then file is saved to r15 and minor versions rgb information is lost and the entity color after loading such file is specified by index 7.
autocad uses different palettes for different backgrounds. for example color with index 7 is white on dark background and black on light background.
btw, autocad adjusts color palette depending on background. for example if you set background to red (255,0,0) color used for index 1 which is usually (255,0,0) wil be rendered with rgb like (247,0,0)
your application can alter color table depending on background like acad.
but if color is specified by rgb its value will be used for rendering regardless of background color.
sergey slezkin