Apple II Graphics Programming (Assembly)

[cerebral_monkey <berkleycameron@gmail.com>]

Hello, I posted here a few months ago asking for help learning
assembly language on the Apple //c (under the handle tomatoes, though
I prefer this one, it is an anagram of my name!). I was hoping that I
might get a little bit more help, specifically where graphics
programming is concerned.

I found a cheetsheet from Beagle Bros that lists useful ROM subroutine
calls, one of these (at $F3F2) is purported to clear the high-
resolution screen that is currently being used. But when I try to use
it, I can't seem to get it to work.

Here is the code that I am trying:

        ORG     $1000

TXTCLR  EQU     $C050   ; text mode off (graphics on)
MIXCLR  EQU     $C052   ; mixed mode off
HISCR   EQU     $C054   ; use HIRES screen 1
HIRES   EQU     $C057   ; HIRES mode on
CLEAR  EQU     $F2F3

        LDY     #$00    ; set graphics modes
        STY     TXTCLR
        STY     MIXCLR
        STY     HIRES
        STY     HISCR
        JSR     CLEAR   ; CLEAR the screen
        TYA
        BRK

Am I doing something wrong here? The screen is still filled with
random data after execution. (I wrote a subroutine to clear the
screen, but the built-in version is probably much faster)

I've got my mind set on re-creating pong, and I noticed that there
were some other useful-looking calls that I might be able to use,
including Hi-Res Colission-Check ($E6). Where might I find more on
these calls and how to use them?

If anyone might direct me to some more information about this, it
would be greatly appreciated! (I just ordered a book called "Assembly
Language for Applesoft Programmers" that should give me a little bit
more info, but I'm impatient, hah )