glMinmax.3G man page
glMinmax — define minmax table
void glMinmax(GLenum target, GLenum internalformat, GLboolean sink);
The minmax table whose parameters are to be set. Must be GL_MINMAX.
The format of entries in the minmax table. Must be one of GL_ALPHA, GL_ALPHA4, GL_ALPHA8, GL_ALPHA12, GL_ALPHA16, GL_LUMINANCE, GL_LUMINANCE4, GL_LUMINANCE8, GL_LUMINANCE12, GL_LUMINANCE16, GL_LUMINANCE_ALPHA, GL_LUMINANCE4_ALPHA4, GL_LUMINANCE6_ALPHA2, GL_LUMINANCE8_ALPHA8, GL_LUMINANCE12_ALPHA4, GL_LUMINANCE12_ALPHA12, GL_LUMINANCE16_ALPHA16, GL_R3_G3_B2, GL_RGB, GL_RGB4, GL_RGB5, GL_RGB8, GL_RGB10, GL_RGB12, GL_RGB16, GL_RGBA, GL_RGBA2, GL_RGBA4, GL_RGB5_A1, GL_RGBA8, GL_RGB10_A2, GL_RGBA12, or GL_RGBA16.
If GL_TRUE, pixels will be consumed by the minmax process and no drawing or texture loading will take place. If GL_FALSE, pixels will proceed to the final conversion process after minmax.
When GL_MINMAX is enabled, the RGBA components of incoming pixels are compared to the minimum and maximum values for each component, which are stored in the two-element minmax table. (The first element stores the minima, and the second element stores the maxima.) If a pixel component is greater than the corresponding component in the maximum element, then the maximum element is updated with the pixel component value. If a pixel component is less than the corresponding component in the minimum element, then the minimum element is updated with the pixel component value. (In both cases, if the internal format of the minmax table includes luminance, then the R color component of incoming pixels is used for comparison.) The contents of the minmax table may be retrieved at a later time by calling glGetMinmax(). The minmax operation is enabled or disabled by calling glEnable() or glDisable(), respectively, with an argument of GL_MINMAX.
glMinmax redefines the current minmax table to have entries of the format specified by internalformat. The maximum element is initialized with the smallest possible component values, and the minimum element is initialized with the largest possible component values. The values in the previous minmax table, if any, are lost. If sink is GL_TRUE, then pixels are discarded after minmax; no further processing of the pixels takes place, and no drawing, texture loading, or pixel readback will result.
glMinmax is present only if ARB_imaging is returned when glGetString() is called with an argument of GL_EXTENSIONS.
GL_INVALID_ENUM is generated if target is not one of the allowable values.
GL_INVALID_ENUM is generated if internalformat is not one of the allowable values.
GL_INVALID_OPERATION is generated if glMinmax is executed between the execution of glBegin() and the corresponding execution of glEnd().
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