HDMI for GameCube and (maybe) Wii?

You said it renders into 640x360. Maybe you mean for letterboxed?

 

When a game enters 16:9 mode it does render 640x360 pixels of the 640x480 framebuffer (assuming square pixel clock).

640/(16/9) = 360

I'm not sure what you mean by letterboxed. In 16:9 mode there are 480-360==120 pixels of letterboxing.

 

I see what you mean. No, the frame is still rendered in 640x480, except the camera/viewport transform squashes the scene horizontally. So it doesn't use a square pixel clock. Of course it's hard to say this generally, Wii/GC is/was often outsourced to secondary teams who may not put too much effort into it.
The games I know more detail of use 640x480 and non-square pixel.

 

??? So you're saying Wii's widescreen isn't anamorphic or that all games horizontally compress the image? (853x480 -> 640x480 via decimation) I've never seen a game horizontally compress the image presumably because a TV cannot autodetect this, I have however seen standard anamorphic compression via letterboxing in multiple games since I regularly use a SDTV and prefer a wider field of view.

Even horizontal compression would suggest the standard square pixel clock, I'm quite certain the pixel clocks are fixed to ~5.36 and ~6.71 MHz derivatives through a least common denominator, a true 16:9 square pixel would be around 8.5 MHz.

 

Yes, Wii widescreen is anamorphic. As in http://en.wikipedia.org/wiki/Anamorphic_widescreen . What the Wii sends to the TV is exactly the same video signal as 4:3, except the TV stretches it back out to 16:9. And pixel are not square. Letterboxing is not anamorphic compression.
The embedded framebuffer can't go over 640x480 (I can't remember the actual limits now). It never renders 853x480, it horizontally scales the geometry that would go into 853x480 into 640x480 before rendering. That has various problems for 2D GUI elements and fonts, but there are many ways to fix, work around or ignore them.
The scart connector supports a signal to switch between widescreen and 4:3, look at pin 8 on http://en.wikipedia.org/wiki/Scart , that's why I was wondering if that is a feature of the Wii DAC.
Nothing stops the game from doing letterboxing manually for displaying 16:9 content on 4:3. Then it does exactly what you describe and renders the screen into 640x360 and adds black bars on top and bottom.

 

I guess the confusion is that I've only seen letterboxed games, not horizontal compression (such as anamorphic DVDs). The standard pixel clock of 27 MHz *is* considered to have square pixels, true widescreen has narrower pixels which expand to be approximately square for the corrected aspect.

BTW, I think it makes more sense to render to 853x480 (backbuffer), then decimate for the framebuffer instead of extra transforms on every single vertex, maybe not if it's implemented in hardware.

 

Exactly like that. Because the pixel clock is fixed on Wii you have it the other way around, they are square when rendered and wider when stretched to widescreen.

 

??? I have it what way around? I've never suggested the pixel clock isn't square. I don't know why we're having a failure to communicate but it's a matter of semantics.

As you now know by "render 640x360 of 640x480" I literally meant to render the scene to a bitmap, not shift out pixels as if to imply there is a physical "640x360 mode" which would be nonstandard for consumer equipment. I also never suggested the framebuffer was 853x480. I now see what you mean by using a camera transform if that effect is possible in order to save on decimation of 853 H pixels.

When you said "The games I know more detail of use 640x480 and non-square pixel" I assumed you meant the pixel clock changes to compensate for widescreen, not that the display renders them rectangularly. I also never suggested that the pixels would be square on the display other than when mentioning a theoretical 8.5 MHz clock which would stretch from narrow to square in anamorphic mode which is what I thought you were suggesting at first. I didn't know any games compressed 16:9 video horizontally to know that you MEANT the display drawing wide rectangular pixels, I've only seen that on special anamorphic DVDs.

All clear hopefully.

 

The Wii does anamorphic display? What games support it? At least in my experience, I always found the Wii simply messes up the aspect ratio, or that it adds letterboxing which causes a loss in lines for the picture which kind of sucks.

 

Is anamorphic 16:9 a matter of changing the frustum so that the far plane is 16:9 and near plane is 4:3?

 

I agreed with you that normally consoles render narrower pixel in widescreen that are stretched to square on a widescreen display. On Wii it is the other way around where it renders square pixel that are stretched wider on display.
You can test this pretty easily by going into the wii display settings and changing the setting to widescreen.
Yes, anamorphic display is a matter of changing the frustum, but not with different near and far planes. The frustum is for a 16:9 wide view into normalised device space 0.0-1.0 in X and Y. That is then scaled to 640x480.