Sets the "gamma function" for the display of each color component\&. Gamma controls the brightness/contrast of colors displayed on the screen\&. A gamma value of 1\&.0 is identity (i\&.e\&., no adjustment is made)\&.
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This function adjusts the gamma based on the "gamma function" parameter, you can directly specify lookup tables for gamma adjustment with \fISDL_SetGammaRamp\fR\&.
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Not all display hardware is able to change gamma\&.
.SH"RETURN VALUE"
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Returns -1 on error (or if gamma adjustment is not supported)\&.