pre_mul_alpha_blend(9)

🎀 NAME 🎀

okay so this is pre_mul_alpha_blend(9) from the Kernel API Manual, and it is literally the alpha blending equation. no cap, the name is pre_mul_alpha_blend — alpha blending equation. 💅

✨ SYNOPSIS ✨

void pre_mul_alpha_blend (const struct line_buffer *stage_buffer ,
struct line_buffer *output_buffer , int x_start , int pixel_count );

🫶 ARGUMENTS 🫶

• stage_buffer — the line with the pixels from src_plane. that’s the source-y bestie.
• output_buffer — a line buffer that receives all the blends output. it’s giving destination energy, fr fr.
• x_start — the start offset. where we begin, periodt.
• pixel_count — the number of pixels to blend. how many pixels we’re serving. ✨

🌈 DESCRIPTION 🌈

okay so the pixels [x_start;x_start+pixel_count) in stage_buffer are blended at [x_start;x_start+pixel_count) in output_buffer. literally the same range, the blend is happening there.

the current DRM assumption is that pixel color values have already been pre-multiplied with the alpha channel values. see more drm_plane_create_blend_mode_property. also, this formula assumes a completely opaque background — like, no sneaky transparency under there, bestie. 💅

🔥 SEE ALSO 🔥

• Kernel file ./drivers/gpu/drm/vkms/vkms_composer.c
• direction_for_rotation(9)
• clamp_line_coordinates(9)
• blend_line(9)
• blend(9)
• vkms_composer_worker(9)

mwah 💖 this page’s source/version is ./drivers/gpu/drm/vkms, dated October 2026, and the manual page is pre_mul_alpha_blend(9). go off, bestie 🎀✨