Hi,
I don't have any clue of the opengl and simgear based stuff, so I looked only
at the struct Building and how to optimize that.
In the attachment you can find 3 structs representing the data.
The original is yours.
'small' is a very small optimization that doesn't require you to map floats to
discrete values. The flags variable holds bool pitched and the building type. I
assumed floors not to be bigger than 65k, so I reduced it to 16 bit ;).
In 'aggressive' I replaced the floats which I think doesn't require the full 4
byte precision of a float. However the mapping from float->int int->float can
take much time depending on the translation function you use. If normal float
division/multiplication is too slow, you could write some functions to directly
accessing the float (shifting the "fraction" depending on the exponent)
(http://en.wikipedia.org/wiki/Single_precision ).
However just ideas on that struct. Sizes in bytes:
original: 44
small: 36
aggressive: 28
Regards,
scosu
On 23.05.2012 11:37, Stuart Buchanan wrote:
> Hi All,
>
> Emilian and Vivian have pointed out a problem with the random
> buildings - they gobble memory. I'd like to get some advice on
> whether there's any solution, and also to ask someone with more C++
> knowledge than myself to take a look at the code and check I'm not
> doing something stupid.
>
> The specific problem scenario is starting a KLAX (Los Angeles) which
> is in the middle of a massive urban area.
>
> Using the default random building density, the tiles that are loaded
> initially when sitting on the runway generates ~ 340k random
> buildings. Each building consists of between 9 and 12 quads (we have a
> "basement" at the bottom to handle slopes, 4 walls, and a roof which
> may be pitched). In turn, each quad has 4 corners, each of which has
> a position (vec3), a normal (vec3) and a texture coordinate (vec2).
>
> So, the absolute minimum memory occupancy of the data for the random
> buildings is 340k * 10 * 4 * 8 = 108MB. On top of that will be some
> OSG overhead and the building texture itself.
>
> Once you start flying more tiles are loaded (presumably well before
> any old tiles are unloaded?) so memory occupancy rapidly increases.
> Flying east from KLAX is particularly bad.
>
> Using a higher building density makes the problem much worse, as you
> need 4X the number of buildings to get double the linear density. I
> ran out of memory on a 4GB system pretty quickly (and tile loading
> takes an age - something I need to look at again).
>
> So
> - Does anyone have any bright ideas on what I can do to reduce the
> base memory occupancy? One option might be to not generate the
> "basement" if the terrain is level.
> - Could a fresh pair of eyes take a look at the obj.cxx, mat.cxx and
> SGBuildingBin.[ch]xx code to see if I've missed something obvious.
>
> Thanks,
>
> -Stuart
>
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#include <stdint.h>
#include <stdio.h>
enum BuildingType {
SMALL = 0,
MEDIUM,
LARGE
};
struct building_original {
enum BuildingType type;
float position[3];
float width;
float depth;
float height;
int floors;
float rotation;
bool pitched;
float radius;
};
#define BUILDING_FLAGS_SMALL 0x01
#define BUILDING_FLAGS_MEDIUM 0x02
#define BUILDING_FLAGS_LARGE 0x04
#define BUILDING_FLAGS_PITCHED 0x08
struct building_small {
uint16_t flags;
uint16_t floors;
float position[3];
float width;
float depth;
float height;
float rotation;
float radius;
};
#pragma pack(push,1)
struct building_aggressive {
float position[3];
uint16_t width;
uint16_t depth;
uint16_t height;
uint16_t rotation;
uint16_t floors;
uint8_t alignment_no_data; // to get better access times for variable radius
uint8_t flags;
uint32_t radius;
};
#pragma pack(pop)
int main(void) {
printf("original: %lu\n", sizeof(struct building_original));
printf("small: %lu\n", sizeof(struct building_small));
printf("aggressive: %lu\n", sizeof(struct building_aggressive));
}
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threat landscape has changed and how IT managers can respond. Discussions
will include endpoint security, mobile security and the latest in malware
threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/
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