PSP homebrew development

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Revision as of 22:53, 20 January 2020 by Mhoskins (talk | contribs) (adding pixel formats)
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Useful Information

Note that while pixel depths are referred to by RGBA below, the actual bit order is BGRA (or BGR for formats without alpha).

Color format is adjustable, but display resolution is fixed when using the PSP display.

Pixel Formats

  • PSP_DISPLAY_PIXEL_FORMAT_8888 - 32-bit RGBA 8:8:8:8 - Full 24-bit color with 8-bit alpha, uses double the VRAM
  • PSP_DISPLAY_PIXEL_FORMAT_4444 - 16-bit RGBA 4:4:4:4 - 12-bit colors, plus 4-bit alpha
  • PSP_DISPLAY_PIXEL_FORMAT_5551 - 16-bit RGBA 5:5:5:1 - 5 bits per color channel, plus boolean alpha (1-bit)
  • PSP_DISPLAY_PIXEL_FORMAT_565 - 16-bit RGBA 5:6:5 - Slightly wider color gamut by bumping green bits to 6, with red and blue using 5 bits

Drawing Pixels

If you're just pushing raw pixels to the screen, there are two ways to do it. There's direct access to the framebuffer: 

u32* vram = (u32*)0x44000000;
sceDisplaySetFrameBuf((void*)vram, 512, PSP_DISPLAY_PIXEL_FORMAT_8888, PSP_DISPLAY_SETBUF_IMMEDIATE);

The VRAM address is 0x04000000, changing the address into 0x04000000 means that reads and writes are uncached. This is slower, but has the advantage that you don't have to sync the cache manually and you're less likely to see graphic artifacts. You can use other memory locations for the framebuffer as well, but the address must be a multiple of 16 bytes.

Calling sceDisplaySetMode() before drawing is also recommended. The code above is for 32-bit mode (8 bits per channel), but other modes are available. Even though the PSP screen is 480 pixels wide, the framebuffer is usually 512 pixels wide to allow for faster address calculation, and as a result faster drawing.

Some of the hardware assisted features you can do with framebuffer include vertical scrolling and page flipping.

Or you can create an array of vertices and draw them using the GPU: 

typedef struct {
	short unsigned u, v;
	short x,y,z;
} Vertex;

Vertex*v=sceGuGetMemory(1*sizeof(Vertex));
v[0].u=0;
v[0].v=0;
v[0].x=240;
v[0].y=136;

sceGuDrawArray(GU_POINTS,GU_TEXTURE_16BIT|GU_VERTEX_16BIT|GU_TRANSFORM_2D,1,0,v);

The GU routines use hardware to perform drawing operations for you. Note that you can draw to different locations, such as a memory buffer or to the framebuffer, in the latter case you'll see the result on screen. This also means it is possible to combine page flipping with hardware assisted drawing, and there's GU routines to help with this. It is important to note that since the GPU is drawing stuff the CPU are free to do other things, also note that you have to consider that the CPU doesn't know what the GPU is doing and vice versa. Because of cache, all textures, vertex lists and such must be in memory before you use them. This means you use a function to invalidate the cache for those memory regions causing any cached data to be written to memory. Again the same data also needs to be in a memory address that is a multiple of 16 bytes, but if you use GU routines to allocate the memory they will take care of this for you. Textures need to be swizzled as well.

Tutorials

Resources

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