I came across some interesting observations regarding the Hyrule Field slowdown. I am going to share my thought here and see what others thoughts on the subject is. This was tested with the Gamecube version of Zelda Twilight Princess, Wii version will be mirrored to the information provided below.
After you beat the forest temple Hyrule Field will be full speeds, when entering the Twilight Hyrule Field will remain at a steady 30 FPS. Collect the tears of light and free Kakariko Village from the Twilight, then try to head up to the Goron Mines.
You'll get knocked down by the Goron, when exiting back into Kakariko Village you will be greeted by Renaldo who informs you to speak to Bo in Ordon Village. Go left (South) and a cutscene will take place. Sieze Epona and then exit to the west into Hyrule Field, notice how Hyrule Field is still a full 30 FPS.
Then go back into Kakariko Village and go north, jump over the gate into the other part of Hyrule Field (The part that you haven't visited yet) Notice that this part of Hyrule Field is about 10 - 15 FPS slower than before.
Now go back into Kakariko Village, go south and west back into the other part of Hyrule Field (West) you were just in, notice anything strange? This part of Hyrule Field (West) you were just in was a solid 30 FPS before visiting the other part of Hyrule Field (North), immediately after visiting the other part of Hyrule Field (North) the other part of Hyrule Field (West) that was a solid 30 FPS will now be 10 - 15 FPS slower than before.
Isn't that a bit strange? As you progress further in the game Hyrule Field becomes slower, so far the slowest I've seen is 10 - 12 FPS.
I'm not sure if vertices or the size of the scene being rendered is the actual problem or if it is a bug that contributes to the slowdown, but I do believe both possibilities should be examined.
After you beat the forest temple Hyrule Field will be full speeds, when entering the Twilight Hyrule Field will remain at a steady 30 FPS. Collect the tears of light and free Kakariko Village from the Twilight, then try to head up to the Goron Mines.
You'll get knocked down by the Goron, when exiting back into Kakariko Village you will be greeted by Renaldo who informs you to speak to Bo in Ordon Village. Go left (South) and a cutscene will take place. Sieze Epona and then exit to the west into Hyrule Field, notice how Hyrule Field is still a full 30 FPS.
Then go back into Kakariko Village and go north, jump over the gate into the other part of Hyrule Field (The part that you haven't visited yet) Notice that this part of Hyrule Field is about 10 - 15 FPS slower than before.
Now go back into Kakariko Village, go south and west back into the other part of Hyrule Field (West) you were just in, notice anything strange? This part of Hyrule Field (West) you were just in was a solid 30 FPS before visiting the other part of Hyrule Field (North), immediately after visiting the other part of Hyrule Field (North) the other part of Hyrule Field (West) that was a solid 30 FPS will now be 10 - 15 FPS slower than before.
Isn't that a bit strange? As you progress further in the game Hyrule Field becomes slower, so far the slowest I've seen is 10 - 12 FPS.
I'm not sure if vertices or the size of the scene being rendered is the actual problem or if it is a bug that contributes to the slowdown, but I do believe both possibilities should be examined.