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<TITLE>Determine the color resolution of screen(256 color, 16 bit, etc)</TITLE>
<META NAME="Author" CONTENT="Harold Howe">
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<H3>
Determine the color resolution of screen(256 color, 16 bit, etc)
</H3>
<P>
The API <TT>GetDeviceCaps</TT> function allows you to determine
the color resolution of the screen. <TT>GetDeviceCaps</TT> takes two arguments;
a handle to a device context and an identifier for the parameter that you want
to find.
</P>
<pre>
<b>int</b> GetDeviceCaps<b>(</b> HDC hdc<b>,</b> <font color="navy">// device-context handle</font>
<b>int</b> nIndex<b>)</b><b>;</b> <font color="navy">// parameter index</font>
</pre>
<P>
In order to call <TT>GetDeviceCaps</TT>, you must provide a handle to a device
context. In other programming environments, you would have to create a DC just
for the sake of calling <TT>GetDeviceCaps</TT>, but in BCB, you can just borrow
the <TT>Handle</TT> property of the form's <TT>Canvas</TT> property. To get the
color resolution, you pass either <TT>BITSPIXEL</TT> or <TT>PLANES</TT> as the
index value. <TT>BITSPIXEL</TT> returns the number of bits used to store the
color of a single pixel. <TT>PLANES</TT> returns the number of color planes
used by the system. Most systems use one color plane and multiple bits to
represent the color of a pixel. Some systems use one pixel with multiple color
planes. Either way, one of the values will be one. You can multiply the return
values to yield one value that represents the color resolution of the system.
</P>
<P>
The following code snippet demonstrates how to determine the color resolution
of the system. As a bonus, it also shows how <TT>GetDeviceCaps</TT> can tell you
directly if a system is using palettes.
</P>
<pre>
<b>int</b> BitsPerPixel <b>=</b> GetDeviceCaps<b>(</b>Canvas<b>-></b>Handle<b>,</b>BITSPIXEL<b>)</b><b>;</b>
<b>int</b> Planes <b>=</b> GetDeviceCaps<b>(</b>Canvas<b>-></b>Handle<b>,</b>PLANES<b>)</b><b>;</b>
BitsPerPixel <b>*</b><b>=</b> Planes<b>;</b> <font color="navy">// either Planes or BitsPerPixel will be</font>
<font color="navy">// equal to 1, so eliminate one of the values.</font>
<b>bool</b> UsesPalettes <b>=</b>
<b>(</b><b>bool</b><b>)</b><b>(</b>GetDeviceCaps<b>(</b>Canvas<b>-></b>Handle<b>,</b> RASTERCAPS<b>)</b> <b>&</b> RC_PALETTE<b>)</b><b>;</b>
<b>if</b><b>(</b>UsesPalettes<b>)</b>
Label1<b>-></b>Caption <b>=</b> <font color="blue">"The screen utilizes palettes"</font><b>;</b>
<b>else</b>
Label1<b>-></b>Caption <b>=</b> <font color="blue">"The screen does not use palettes"</font><b>;</b>
<b>switch</b> <b>(</b>BitsPerPixel<b>)</b>
<b>{</b>
<b>case</b> <font color="blue">24</font><b>:</b>
Label2<b>-></b>Caption <b>=</b> <font color="blue">"24-bit true color"</font><b>;</b>
<b>break</b><b>;</b>
<b>case</b> <font color="blue">16</font><b>:</b>
Label2<b>-></b>Caption <b>=</b> <font color="blue">"16-bit high color"</font><b>;</b>
<b>break</b><b>;</b>
<b>case</b> <font color="blue">8</font><b>:</b>
Label2<b>-></b>Caption <b>=</b> <font color="blue">"256 color mode"</font><b>;</b>
<b>break</b><b>;</b>
<b>case</b> <font color="blue">4</font><b>:</b>
Label2<b>-></b>Caption <b>=</b> <font color="blue">"16 color mode"</font><b>;</b>
<b>break</b><b>;</b>
<b>case</b> <font color="blue">1</font><b>:</b>
Label2<b>-></b>Caption <b>=</b> <font color="blue">"Monochrome mode"</font><b>;</b>
<b>break</b><b>;</b>
<b>default</b><b>:</b>
Label2<b>-></b>Caption <b>=</b> <font color="blue">"The screen supports "</font> <b>+</b> IntToStr<b>(</b><font color="blue">1</font><b><<</b> BitsPerPixel<b>)</b> <b>+</b>
<font color="blue">" different colors"</font><b>;</b>
<b>break</b><b>;</b>
<b>}</b>
</pre>
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