base:spritevectors
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base:spritevectors [2016-12-09 12:53] – [The data exporter] bitbreaker | base:spritevectors [2016-12-09 17:17] – [Adding the Wurstglanz] bitbreaker | ||
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===== Sprite vectors ===== | ===== Sprite vectors ===== | ||
- | Basically one can also draw edges by displaying sprites and manipulating | + | Basically one can also draw edges by displaying sprites and manipulating |
As a first step, we can expand all sprites in X and Y to achieve more effect area, but this is still not satisfactory. As we inspect the shape of a cube, we notice, that it maximum has 3 edges on the left side and a final edge at the right to separate it from the background. So if we manage to display those 4 edges with 4 sprites, we are already on a good way and only need to change 4 x-positions per rasterline, do we? | As a first step, we can expand all sprites in X and Y to achieve more effect area, but this is still not satisfactory. As we inspect the shape of a cube, we notice, that it maximum has 3 edges on the left side and a final edge at the right to separate it from the background. So if we manage to display those 4 edges with 4 sprites, we are already on a good way and only need to change 4 x-positions per rasterline, do we? | ||
As for the height, we can make use of the sprite stretching trick to make the sprites up to 200 pixels high or even beyond. Happily, this trick also gives us other advantages, as we can switch sprites on/off by omitting a stretch for a single sprite at any given line. Means, our timing over the whole screen will stay the same for each rasterline and thus we can easily use unrolled display code. | As for the height, we can make use of the sprite stretching trick to make the sprites up to 200 pixels high or even beyond. Happily, this trick also gives us other advantages, as we can switch sprites on/off by omitting a stretch for a single sprite at any given line. Means, our timing over the whole screen will stay the same for each rasterline and thus we can easily use unrolled display code. | ||
+ | |||
+ | {{: | ||
+ | |||
+ | This is what sprites look like unexpanded. If only first line is stretched, nothing is displayed, if first line is skipped, display of solid lines start until also this line is skipped in the stretcher. | ||
{{: | {{: | ||
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====== Y-movement ====== | ====== Y-movement ====== | ||
- | The display code is entered at the right offset at the right rasterline and is left after the full height of the object being displayed. | + | The display code is entered at the right offset at the right rasterline and is left after the full height of the object being displayed. The entry can only happen on full charlines, as sprite display and badline supression can only work from there on. So some offsetting wizardry has to be added (rough y position charline-wise, |
====== Precalced flat slopes ====== | ====== Precalced flat slopes ====== | ||
Flat slopes are stores in slope tables. To save space, each slope is references with a pointer. Thus, we have the possibility to also reference parts of other slopes in case of matches and save memory. | Flat slopes are stores in slope tables. To save space, each slope is references with a pointer. Thus, we have the possibility to also reference parts of other slopes in case of matches and save memory. | ||
+ | The slope code plots directly into the ldx/y statements of the display-code one value per codeblock/ | ||
- | ====== Bresenham vs. fixed point math ====== | + | < |
+ | sbc (slope), | ||
+ | iny | ||
+ | sta sprite1_pos + .x * dcode_size, | ||
+ | </ | ||
- | Bresenham can be done pretty fast, but when doing fixed point we are even faster and the accuracy bears still enough potential to not cause glitches. | + | Thus we save on code and only need unrolled code for increasing and decreasing slopes. Way less than for the steep case! |
+ | ====== Steep slopes - Bresenham vs. fixed point math ====== | ||
+ | |||
+ | Bresenham can be done pretty fast, but when doing fixed point we are even faster and the accuracy bears still enough potential to not cause glitches. | ||
+ | |||
+ | < | ||
+ | sbc frac | ||
+ | bcs + | ||
+ | inx | ||
+ | + | ||
+ | stx sprite1_pos + .x * dcode_size | ||
+ | </ | ||
====== The data exporter ====== | ====== The data exporter ====== | ||
- | The nifty part is to write a data exporter that sorts all edges from left to right and calculates the dimensions of the gap sprites. Also this data should be as tiny as possible. | + | The nifty part is to write a data exporter that runs through |
====== Adding the Wurstglanz ====== | ====== Adding the Wurstglanz ====== | ||
Line 79: | Line 99: | ||
to be continued soon... | to be continued soon... | ||
+ | ====== Future work / outlook ====== | ||
+ | If the badline-supression is done per frame and not per line (but black background then) the ratio of edge building sprites and gap sprites can be shifted towards more edges, as more x-position writes can happen. Also this technique peaks on frames where a lot of nearly 45° slopes happen, else quite some rastertime is left, but on peaks (SID included) only 3 rasterlines are left at maximum size of 160x160. Also if going one pixel beyond in size, 3 gap sprites are needed for a single face and we run out of sprites anyway :-) |
base/spritevectors.txt · Last modified: 2020-07-28 08:42 by bitbreaker