-/*
- * Calculate fog coords from window z values
- * Input: n - number of pixels
- * z - array of integer depth values
- * red, green, blue, alpha - pixel colors
- * Output: red, green, blue, alpha - fogged pixel colors
- *
- * Use lookup table & interpolation?
+
+/**
+ * Template code for computing fog blend factor and applying it to colors.
+ * \param TYPE either GLubyte, GLushort or GLfloat.
+ * \param COMPUTE_F code to compute the fog blend factor, f.
+ */
+#define FOG_LOOP(TYPE, FOG_FUNC) \
+if (span->arrayAttribs & VARYING_BIT_FOGC) { \
+ GLuint i; \
+ for (i = 0; i < span->end; i++) { \
+ const GLfloat fogCoord = span->array->attribs[VARYING_SLOT_FOGC][i][0]; \
+ const GLfloat c = fabsf(fogCoord); \
+ GLfloat f, oneMinusF; \
+ FOG_FUNC(f, c); \
+ f = CLAMP(f, 0.0F, 1.0F); \
+ oneMinusF = 1.0F - f; \
+ rgba[i][RCOMP] = (TYPE) (f * rgba[i][RCOMP] + oneMinusF * rFog); \
+ rgba[i][GCOMP] = (TYPE) (f * rgba[i][GCOMP] + oneMinusF * gFog); \
+ rgba[i][BCOMP] = (TYPE) (f * rgba[i][BCOMP] + oneMinusF * bFog); \
+ } \
+} \
+else { \
+ const GLfloat fogStep = span->attrStepX[VARYING_SLOT_FOGC][0]; \
+ GLfloat fogCoord = span->attrStart[VARYING_SLOT_FOGC][0]; \
+ const GLfloat wStep = span->attrStepX[VARYING_SLOT_POS][3]; \
+ GLfloat w = span->attrStart[VARYING_SLOT_POS][3]; \
+ GLuint i; \
+ for (i = 0; i < span->end; i++) { \
+ const GLfloat c = fabsf(fogCoord) / w; \
+ GLfloat f, oneMinusF; \
+ FOG_FUNC(f, c); \
+ f = CLAMP(f, 0.0F, 1.0F); \
+ oneMinusF = 1.0F - f; \
+ rgba[i][RCOMP] = (TYPE) (f * rgba[i][RCOMP] + oneMinusF * rFog); \
+ rgba[i][GCOMP] = (TYPE) (f * rgba[i][GCOMP] + oneMinusF * gFog); \
+ rgba[i][BCOMP] = (TYPE) (f * rgba[i][BCOMP] + oneMinusF * bFog); \
+ fogCoord += fogStep; \
+ w += wStep; \
+ } \
+}
+
+/**
+ * Apply fog to a span of RGBA pixels.
+ * The fog value are either in the span->array->fog array or interpolated from
+ * the fog/fogStep values.
+ * They fog values are either fog coordinates (Z) or fog blend factors.
+ * _PreferPixelFog should be in sync with that state!