Re: [PATCH 1/4] drm: add plane support

From: Marcus Lorentzon <marcus.xm.lorentzon@stericsson.com>
To: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: "intel-gfx@lists.freedesktop.org"
	<intel-gfx@lists.freedesktop.org>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH 1/4] drm: add plane support
Date: Wed, 8 Jun 2011 11:41:17 +0200	[thread overview]
Message-ID: <4DEF43BD.8040606@stericsson.com> (raw)
In-Reply-To: <20110607140121.279bf9b4@jbarnes-desktop>

On 06/07/2011 11:01 PM, Jesse Barnes wrote:
> On Tue,  7 Jun 2011 13:07:39 -0700
> Jesse Barnes<jbarnes@virtuousgeek.org>  wrote:
>
>    
>> +/* Planes blend with or override other bits on the CRTC */
>> +struct drm_mode_set_plane {
>> +	__u32 plane_id;
>> +	__u32 crtc_id;
>> +	__u32 fb_id; /* contains surface format type */
>> +
>> +	__u32 crtc_x, crtc_y;
>> +	__u32 x, y;
>> +
>> +	/* FIXME: color key/mask, scaling, z-order, other? */
>> +};
>>      
> Forgot to add the scaling factors to this.  Would:
>    __u32 scaling_x; /* fixed 16.16 format */
>    __u32 scaling_y;
> work for people?
>    

If you want to pan around in zoomed in video/viewfinder/snapshots it 
might be better to have a fixed 16.16 source rectangle and a integer 
destination rectangle. That way you can move around the zoomed in source 
rectangle in small increments and upscale it to destination rectangle 
(and skip fractions if HW don't support it). For example, if you zoom 4x 
and have only fixed 16.16 scaling factor, you still get the the integer 
fb (x, y) position in the top left corner (crtc_x, crtc_y) of the 
overlay. And when you pan in the overlay, you will have to move source 
rectangle in 4 destination pixel increments. So what about this instead:

__u32 x, y, src_w, src_h; /* fixed 16.16 */
__u32 crtc_x, crtc_y, crtc_w, crtc_h;

Maybe rename x, y to src_x, src_y? crtc_w/h is needed to define zoom 
factor (scaling_[wh] = crtc_[wh] / src_[wh]).

So the "zoom transform" would be defined by (src_x, src_y, src_w, src_h) 
=> (crtc_x, crtc_y, crtc_w, crtc_h)

It also gets rid of how to handle corner cases where scaling factor 
defines a source area outside source fb. Now you can just say both rect 
has to be inside crtc/fb. And you can also animate/move/clip a zoomed 
overlay off screen without picture jumping (fb and display coords don't 
align when zoomed).

Summary, rectangles allow more precise representation of zoom factor, 
and 16.16 source coords for stable image when moving overlay off screen 
(clipping) or panning overlay content.

BTW. Why not just add "__s32 z;" too? drm_mode_set_plane seems to be 
plane position setup.

/BR
/Marcus