u/distortion: A stab in the dark to try and improve Index chromatic aberration

src/xrt/auxiliary/util/u_distortion_mesh.c

@@ -144,6 +144,10 @@ u_compute_distortion_vive(struct u_vive_values *values, float u, float v, struct
 		float r2 = m_vec2_dot(texCoord, texCoord);
 		float d_inv =
 		    ((r2 * val.coefficients[i][2] + val.coefficients[i][1]) * r2 + val.coefficients[i][0]) * r2 + 1.0;
+
+		// The scaled part of DISTORT_DPOLY3_SCALED, seems to improve chromatic abberation.
+		d_inv -= val.coefficients[i][3];
+
 		float d = 1.0 / d_inv;
 
 		struct xrt_vec2 offset = {0.5, 0.5};

src/xrt/auxiliary/util/u_distortion_mesh.h

@@ -75,8 +75,8 @@ struct u_vive_values
 	//! r/g/b
 	struct xrt_vec2 center[3];
 
-	//! r/g/b, a/b/c
-	float coefficients[3][3];
+	//! r/g/b, a/b/c/d
+	float coefficients[3][4];
 };
 
 /*!

src/xrt/drivers/ohmd/oh_device.c

@@ -634,32 +634,38 @@ oh_device_create(ohmd_context *ctx, ohmd_device *dev, const char *prod)
 		ohd->distortion.vive[0].coefficients[0][0] = -0.188236068524731f;
 		ohd->distortion.vive[0].coefficients[0][1] = -0.221086205321053f;
 		ohd->distortion.vive[0].coefficients[0][2] = -0.2537849057915209f;
+		ohd->distortion.vive[0].coefficients[0][3] = 0.0f;
 
 		// blue
 		ohd->distortion.vive[0].coefficients[1][0] = -0.07316590815739493f;
 		ohd->distortion.vive[0].coefficients[1][1] = -0.02332400789561968f;
 		ohd->distortion.vive[0].coefficients[1][2] = 0.02469959434698275f;
+		ohd->distortion.vive[0].coefficients[1][3] = 0.0f;
 
 		// red
 		ohd->distortion.vive[0].coefficients[2][0] = -0.02223805567703767f;
 		ohd->distortion.vive[0].coefficients[2][1] = -0.04931309279533211f;
 		ohd->distortion.vive[0].coefficients[2][2] = -0.07862881939243466f;
+		ohd->distortion.vive[0].coefficients[2][3] = 0.0f;
 
 		// right
 		// green
 		ohd->distortion.vive[1].coefficients[0][0] = -0.1906209981894497f;
 		ohd->distortion.vive[1].coefficients[0][1] = -0.2248896677207884f;
 		ohd->distortion.vive[1].coefficients[0][2] = -0.2721364516782803f;
+		ohd->distortion.vive[1].coefficients[0][3] = 0.0f;
 
 		// blue
 		ohd->distortion.vive[1].coefficients[1][0] = -0.07346071902951497f;
 		ohd->distortion.vive[1].coefficients[1][1] = -0.02189527566250131f;
 		ohd->distortion.vive[1].coefficients[1][2] = 0.0581378652359256f;
+		ohd->distortion.vive[1].coefficients[1][3] = 0.0f;
 
 		// red
 		ohd->distortion.vive[1].coefficients[2][0] = -0.01755850332081247f;
 		ohd->distortion.vive[1].coefficients[2][1] = -0.04517245633373419f;
 		ohd->distortion.vive[1].coefficients[2][2] = -0.0928909347763f;
+		ohd->distortion.vive[1].coefficients[2][3] = 0.0f;
 		// clang-format on
 
 		ohd->base.compute_distortion = compute_distortion_vive;

src/xrt/drivers/survive/survive_driver.c

@@ -895,16 +895,15 @@ _json_get_int(const cJSON *json, const char *name)
 static void
 _get_color_coeffs(struct u_vive_values *values, const cJSON *coeffs, uint8_t eye, uint8_t channel)
 {
-	// this is 4 on index, all values populated
-	// assert(coeffs->length == 8);
-	// only 3 coeffs contain values
+	// For Vive this is 8 with only 3 populated.
+	// For Index this is 4 with all values populated.
 	const cJSON *item = NULL;
 	size_t i = 0;
 	cJSON_ArrayForEach(item, coeffs)
 	{
 		values->coefficients[channel][i] = (float)item->valuedouble;
 		++i;
-		if (i == 3) {
+		if (i == 4) {
 			break;
 		}
 	}

src/xrt/drivers/vive/vive_config.c

@@ -30,16 +30,15 @@
 static void
 _get_color_coeffs(struct u_vive_values *values, const cJSON *coeffs, uint8_t eye, uint8_t channel)
 {
-	// this is 4 on index, all values populated
-	// assert(coeffs->length == 8);
-	// only 3 coeffs contain values
+	// For Vive this is 8 with only 3 populated.
+	// For Index this is 4 with all values populated.
 	const cJSON *item = NULL;
 	size_t i = 0;
 	cJSON_ArrayForEach(item, coeffs)
 	{
 		values->coefficients[channel][i] = (float)item->valuedouble;
 		++i;
-		if (i == 3) {
+		if (i == 4) {
 			break;
 		}
 	}