Direct framebuffer access

set_pixel() is convenient for teaching and small effects. For a software renderer or an engine port, access the framebuffer directly.

uint8_t *pixels = framebuffer();
int pitch = screen_pitch();

pixels[y * pitch + x] = color;

In indexed mode the pitch is normally equal to the screen width because each pixel is one byte. Use screen_pitch() rather than assuming that relationship in generic code.

RGB565

uint8_t *pixels = framebuffer();
uint16_t *row = (uint16_t *)(pixels + y * screen_pitch());
row[x] = rgb565_pack(255, 128, 0);

RGB24

Each pixel occupies three bytes in RGB order:

uint8_t *pixels = framebuffer();
uint8_t *p = pixels + y * screen_pitch() + x * 3;
p[0] = r;
p[1] = g;
p[2] = b;

RGBA32

Each pixel occupies four bytes in RGBA order.

Mode changes

screen_set_mode() allocates a new framebuffer. A pointer obtained before the change is no longer valid:

screen_set_mode(320, 200, pixel_indexed8);
uint8_t *pixels = framebuffer();

This direct-memory API is the part of PixelRAM intended for substantial software renderers and ports such as DOOM and Descent.