KMSDRM: Allow setting scaling sharpness with env var

By setting SDL_VIDEO_KMSDRM_SCALING_SHARPNESS to an integer value before
flipping the buffers, it is now possible to control the sharpness of the
scaling.

0: nearest-neighbour
1: bilinear filtering
2-32: bicubic filtering.

If not provided, the default value is 8.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>

Author: pcercuei

src/video/kmsdrm/SDL_kmsdrmvideo.c

@@ -324,11 +324,14 @@ static int KMSDRM_SetCrtcParams(_THIS, drmModeAtomicReqPtr req, Uint32 plane_id,
 				Uint32 crtc_id, int width, int height,
 				int mode_width, int mode_height, int bpp)
 {
-	unsigned int crtc_w, crtc_h, scaling_mode = this->hidden->scaling_mode;
+	unsigned int crtc_w, crtc_h, scaling_mode = this->hidden->scaling_mode, sharpness = 8;
 	const char *env_mode = getenv("SDL_VIDEO_KMSDRM_SCALING_MODE");
+	const char *env_sharpness = getenv("SDL_VIDEO_KMSDRM_SCALING_SHARPNESS");
 
 	if (env_mode)
 		scaling_mode = atoi(env_mode);
+	if (env_sharpness)
+		sharpness = atoi(env_sharpness);
 
 	switch (scaling_mode) {
 	case DRM_SCALING_MODE_ASPECT_RATIO:
@@ -362,6 +365,9 @@ static int KMSDRM_SetCrtcParams(_THIS, drmModeAtomicReqPtr req, Uint32 plane_id,
 		return 1;
 	}
 
+	if (!add_property(this, req, plane_id, "sharpness", 1, sharpness))
+		return 1;
+
 	if (!add_property(this, req, plane_id, "CRTC_X", 0, (mode_width - crtc_w) / 2))
 		return 1;