colorramp: Use supplied gamma ramps as initial value

This changes colorramp_fill() to base the ramp calculations on the
existing values in the supplied tables, instead of basing it on a pure
`i/size` value computed on the fly.

All gamma adjustment methods are changed to explicitly initialize the ramps
to the `i/size` value before calls to colorramp_fill().

src/colorramp.c

@@ -297,9 +297,12 @@ colorramp_fill(uint16_t *gamma_r, uint16_t *gamma_g, uint16_t *gamma_b,
 			  &blackbody_color[temp_index+3], white_point);
 
 	for (int i = 0; i < size; i++) {
-		gamma_r[i] = F((float)i/size, 0) * (UINT16_MAX+1);
-		gamma_g[i] = F((float)i/size, 1) * (UINT16_MAX+1);
-		gamma_b[i] = F((float)i/size, 2) * (UINT16_MAX+1);
+		gamma_r[i] = F((double)gamma_r[i]/(UINT16_MAX+1), 0) *
+			(UINT16_MAX+1);
+		gamma_g[i] = F((double)gamma_g[i]/(UINT16_MAX+1), 1) *
+			(UINT16_MAX+1);
+		gamma_b[i] = F((double)gamma_b[i]/(UINT16_MAX+1), 2) *
+			(UINT16_MAX+1);
 	}
 }
 
@@ -315,9 +318,9 @@ colorramp_fill_float(float *gamma_r, float *gamma_g, float *gamma_b,
 			  &blackbody_color[temp_index+3], white_point);
 
 	for (int i = 0; i < size; i++) {
-		gamma_r[i] = F((float)i/size, 0);
-		gamma_g[i] = F((float)i/size, 1);
-		gamma_b[i] = F((float)i/size, 2);
+		gamma_r[i] = F((double)gamma_r[i], 0);
+		gamma_g[i] = F((double)gamma_g[i], 1);
+		gamma_b[i] = F((double)gamma_b[i], 2);
 	}
 }
 

src/gamma-drm.c

@@ -268,6 +268,16 @@ drm_set_temperature(drm_state_t *state, const color_setting_t *setting)
 			}
 			last_gamma_size = crtcs->gamma_size;
 		}
+
+		/* Initialize gamma ramps to pure state */
+		int ramp_size = crtcs->gamma_size;
+		for (int i = 0; i < ramp_size; i++) {
+			uint16_t value = (double)i/ramp_size * (UINT16_MAX+1);
+			r_gamma[i] = value;
+			g_gamma[i] = value;
+			b_gamma[i] = value;
+		}
+
 		colorramp_fill(r_gamma, g_gamma, b_gamma, crtcs->gamma_size,
 			       setting);
 		drmModeCrtcSetGamma(state->fd, crtcs->crtc_id, crtcs->gamma_size,

src/gamma-quartz.c

@@ -96,6 +96,14 @@ quartz_set_temperature_for_display(CGDirectDisplayID display,
 	float *gamma_g = &gamma_ramps[1*ramp_size];
 	float *gamma_b = &gamma_ramps[2*ramp_size];
 
+	/* Initialize gamma ramps to pure state */
+	for (int i = 0; i < ramp_size; i++) {
+		float value = (double)i/ramp_size;
+		gamma_r[i] = value;
+		gamma_g[i] = value;
+		gamma_b[i] = value;
+	}
+
 	colorramp_fill_float(gamma_r, gamma_g, gamma_b, ramp_size,
 			     setting);
 

src/gamma-randr.c

@@ -327,6 +327,14 @@ randr_set_temperature_for_crtc(randr_state_t *state, int crtc_num,
 	uint16_t *gamma_g = &gamma_ramps[1*ramp_size];
 	uint16_t *gamma_b = &gamma_ramps[2*ramp_size];
 
+	/* Initialize gamma ramps to pure state */
+	for (int i = 0; i < ramp_size; i++) {
+		uint16_t value = (double)i/ramp_size * (UINT16_MAX+1);
+		gamma_r[i] = value;
+		gamma_g[i] = value;
+		gamma_b[i] = value;
+	}
+
 	colorramp_fill(gamma_r, gamma_g, gamma_b, ramp_size,
 		       setting);
 

src/gamma-vidmode.c

@@ -180,6 +180,14 @@ vidmode_set_temperature(vidmode_state_t *state,
 	uint16_t *gamma_g = &gamma_ramps[1*state->ramp_size];
 	uint16_t *gamma_b = &gamma_ramps[2*state->ramp_size];
 
+	/* Initialize gamma ramps to pure state */
+	for (int i = 0; i < state->ramp_size; i++) {
+		uint16_t value = (double)i/state->ramp_size * (UINT16_MAX+1);
+		gamma_r[i] = value;
+		gamma_g[i] = value;
+		gamma_b[i] = value;
+	}
+
 	colorramp_fill(gamma_r, gamma_g, gamma_b, state->ramp_size,
 		       setting);
 

src/gamma-w32gdi.c

@@ -153,6 +153,14 @@ w32gdi_set_temperature(w32gdi_state_t *state,
 	WORD *gamma_g = &gamma_ramps[1*GAMMA_RAMP_SIZE];
 	WORD *gamma_b = &gamma_ramps[2*GAMMA_RAMP_SIZE];
 
+	/* Initialize gamma ramps to pure state */
+	for (int i = 0; i < GAMMA_RAMP_SIZE; i++) {
+		WORD value = (double)i/GAMMA_RAMP_SIZE * (UINT16_MAX+1);
+		gamma_r[i] = value;
+		gamma_g[i] = value;
+		gamma_b[i] = value;
+	}
+
 	colorramp_fill(gamma_r, gamma_g, gamma_b, GAMMA_RAMP_SIZE,
 		       setting);