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26 lines
1.1 KiB
Markdown
26 lines
1.1 KiB
Markdown
perform a shifted blit
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======================
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Extending [007.masked_blit](../007.masked_blit), we now add the capability to blit to non word aligned columns.
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The blitter can only address word aligned screen positions. This makes drawing something on a non word aligned boundary slightly more complex.
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So the algorithm for drawing to non word aligned boundaries is as follows:
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1. The destination address is the word aligned address to the left of the desired position.
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2. Command the blitter to blit an extra word to the right of our blitter object.
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3. We mask the trailing word of each line to prevent the extra word from being blit.
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4. We right shift the data by the difference in bits between the desired column and the word aligned column from (1).
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5. We make the line modulos #-2 so blitter object data is correctly fetched.
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[Download disk image](bin/shift_blit.adf?raw=true)
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screenshot
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----------
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try it
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------
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* [Download disk image](bin/shift_blit.adf?raw=true)
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* <a href="http://alpine9000.github.io/ScriptedAmigaEmulator/#amiga_examples/shift_blit.adf" target="_blank">Run in SAE</a>
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