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36 lines
1.7 KiB
Markdown
36 lines
1.7 KiB
Markdown
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Tutorial 09 - Framebuffer
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=========================
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Okay, finaly some eyecandy :-) So far the screen was blank. Now we're about to change the resolution with
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several tags in a single mbox_call, then display a pixmap. I've put a lot of comments for each tag and
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argument to help you, see lfb.c. But at the end of the day it's nothing more than filling up an int array
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and call mbox_call, really simple. If you wish, you can try to remove or add more tags to the message and
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see what happens. Could have used MBOX_CH_FB (FrameBuffer channel), but MBOX_CH_PROP gives us more flexibility.
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Important note on pitch: maybe you don't know, but video screens does not necessairly map raster lines
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continously in memory. For example it is possible that 800 pixels (800*4=3200 bytes) are stored in 4096
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bytes for every line. Therefore it's important to use the queried pitch value instead of width*4 when
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calculating the postition for the Y coordinate.
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Also note that the GPU on the Raspberry Pi is very powerful. You can create a large virtual screen (let's say
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65536x768) but display only 1024x768 pixels at once. With mailbox messages you can move that window very fast
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without the need of copying pixel buffers, thus creating a smooth scrolling effect. In this tutorial both
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virtual screen and physical screen is set to 1024x768.
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Lfb.h, lfb.c
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------------
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`lfb_init()` sets up resolution, depth, and color channel order. Also queries framebuffer's address.
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`lfb_showpicture()` displays a picture in the center of the screen by drawing pixels to the framebuffer.
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Homer.h
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-------
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The pixmap, saved with the Gimp as C header file. No compression, pixels are stored one-by-one.
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Main
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----
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Very simple. We set the resolution and display the picture, that's all.
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