Saturday, 13 August 2011

Let's bounce

Saturday 13th August 2011

I am feeling afresh from my 2 week break in Somerset. Now I am ready for some more programming and music composing. On Thursday (Although I didn't mention it in the blog) I have been drawing some test graphics and sprites for the "Horizontal scrolling platform framework" for the 16KB cartridge game for the RGCD competition, which is currently in progress (And I am aiming to get it released down there in November). I also designed a map for the framework. Looks very basic and sort of rubbish graphics, but well, it's not the actual game graphics for Woolly Jumper. As Shaun's working on those :)

Today I felt like doing some more programming on the platform scroll engine. Although on Thursday I did add the new map to the project, I decided to update the scroll engine slightly. It appeared that I was using the KERNAL IRQ vectors, using #$37 as the $01 value. Because this was limited. I decided to switch off the basic KERNAL vectors, by simply changing the value of $01 to #$35 and then I changed all $0314 and $0315 vectors to $fffe and $ffff. I also add pointers to $fffa and $fffb to disable the RESTORE key from crashing the program. As soon as I was happy with the interrupts, I added an extra interrupt in which uses a standard multicolour for the water, and also a different colour scheme for the platforms. I made the default map colour to use a red scheme. Okay, not really bad. :) I tested the scroll and the scroll seems to work well.

There appears to be something missing. Those of which are SPRITES :). I imported the test sprites into the source code, as raw sprites. Then I got the sprites to display on to the screen. Well, just the player sprite for now that is :). Next I worked on the joystick read routine, so that the player can move up/down left or right (no shooting yet). Once I did that, the next job was to program in the self-modifying Sprite to background collision detection. So I check the value of the character sets which were being used for the top of the platform. The basic idea is to test to see if the player touches any part of the upper charset that represents the platform (anywhere on screen). If the player touches it, the sheep will flash until it is off the background.

After testing the routine was working, I programmed some additional routines that will make the sheep jump continuously. So that I could get the jumping slightly more at an accurate level. After a lot of tweaking with the jumping routine, I altered the joystick routine even more and got the player jumping and falling perfectly. Finally I added the moving aliens (Which still require a variety of movements, which will be implemented later on this week.) I also enabled the player to be able to fire bullets as well. After assembly of the framework so far, things are starting to take shape quite nicely. Enjoy the video! :)
video

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