| shams said: The XBOX has a shared memory architecture - meaning more memory could be allocated to the frame buffer - which is needed for 720p / 1080i resolutions. The Wii doesn't have this. The lack of VRAM is the biggest reason why the Wii will struggle to do 720p. 720 --> 1280 x 720 pixels = 920,000 pixels (approx). If the Wii *is* limited to only 3MB of frame buffer memory (unless there is some trick), that's just not enough memory. Usually (at a minimum) you want 16bit colour + 8bit zbuffer (can be skipped sometimes) - and at least TWO buffer. Otherwise its drawing from the buffer as you are changing things. (maybe you can setup a buffer not in VRAM - but this may not work on the Wii very well - I don't have the exact docs, so not sure). This also leaves NO memory for textures. ... From a memory point-of-view - its possible - but very hard technically. It may also seriously cripple whatever you are doing quality-wise. |
First let's make it clear what "VRAM" means. The Wii has 64 MB of main memory and 24 MB of graphics memory (VRAM). It also has the 3 MB of embedded memory on the Hollywood die.
Now let's talk double buffering. The back buffer (where you do your drawing) resides in the embedded memory. The front buffer (what's on the screen) resides in graphics memory. Most of the reason for having an embedded framebuffer is to facilitate overdraw, z-buffer reads, and especially alpha blending and other types of blending operations (see games like Metroid Prime for extreme use of framebuffer effects). Once you actually get the finished scene, copying it to the front buffer consumes very little bandwidth -- at most, 180 MB/s (3 MB * 60 fps). At any rate, you only need one buffer in the embedded memory.
Also, if you do need more pixels than you can cram in there, you can always render the top half of a scene in 1280x360 to the embedded memory, copy it to the front buffer, then move the front buffer pointer forward, and do it again for the bottom half. This is basically the equivalent of doing 480p at 120 frames per second. Of course, if your 720p game only needs to run at 30 fps, then it would be the equivalent of doing 480p at 60 fps, something a lot of Wii games already do.
