Re: [PATCH v3 07/12] lib/igt_color: Add YUV pixel reading support

[Alex Hung <alex.hung@amd.com>]

Reviewed-by: Alex Hung <alex.hung@amd.com>

On 6/23/26 11:57, Harry Wentland wrote:
> Add functions to read YUV pixel values from framebuffers. Supports
> NV12 and P010 formats with proper handling of:
> - Multi-planar Y/UV data layout
> - 8-bit and 10-bit sample depths
> - Chroma subsampling
> 
> This provides the foundation for YUV color transformation testing.
> 
> Assisted-by: Claude:claude-sonnet-4-5
> Signed-off-by: Harry Wentland <harry.wentland@amd.com>
> ---
>   lib/igt_color.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 72 insertions(+)
> 
> diff --git a/lib/igt_color.c b/lib/igt_color.c
> index 8c405275acf8..a451f5642bac 100644
> --- a/lib/igt_color.c
> +++ b/lib/igt_color.c
> @@ -259,6 +259,78 @@ void igt_color_multiply_inv_125(igt_pixel_t *pixel)
>   	igt_color_multiply(pixel, 1 / 125.0f);
>   }
>   
> +/**
> + * igt_color_extract_yuv_pixel - Extract raw Y, U, V values from YUV buffer
> + * @fb: framebuffer
> + * @x: x coordinate
> + * @y: y coordinate
> + * @y_plane: pointer to Y plane
> + * @uv_plane: pointer to UV plane
> + * @y_stride: stride of Y plane
> + * @uv_stride: stride of UV plane
> + * @out_y: output Y value (raw, not normalized)
> + * @out_u: output U value (raw, not normalized)
> + * @out_v: output V value (raw, not normalized)
> + *
> + * Extracts raw Y, U, V component values from a YUV framebuffer at the given
> + * coordinates. Handles 4:2:0 subsampling for UV components. Values are raw
> + * (not normalized) and format-specific.
> + */
> +static void
> +igt_color_extract_yuv_pixel(igt_fb_t *fb, int x, int y,
> +			    uint8_t *y_plane, uint8_t *uv_plane,
> +			    int y_stride, int uv_stride,
> +			    uint32_t *out_y, uint32_t *out_u, uint32_t *out_v)
> +{
> +	if (fb->drm_format == DRM_FORMAT_NV12) {
> +		*out_y = y_plane[y * y_stride + x];
> +		*out_u = uv_plane[(y / 2) * uv_stride + (x / 2) * 2 + 0];
> +		*out_v = uv_plane[(y / 2) * uv_stride + (x / 2) * 2 + 1];
> +	} else if (fb->drm_format == DRM_FORMAT_P010) {
> +		uint16_t *y16 = (uint16_t *)y_plane;
> +		uint16_t *uv16 = (uint16_t *)uv_plane;
> +
> +		*out_y = y16[y * (y_stride / 2) + x];
> +		*out_u = uv16[(y / 2) * (uv_stride / 2) + (x / 2) * 2 + 0];
> +		*out_v = uv16[(y / 2) * (uv_stride / 2) + (x / 2) * 2 + 1];
> +	} else {
> +		igt_skip("YUV pixel format support not implemented");
> +	}
> +}
> +
> +/**
> + * igt_color_yuv_to_pixel - Convert raw Y, U, V values to normalized pixel
> + * @drm_format: YUV format (NV12 or P010)
> + * @raw_y: raw Y value
> + * @raw_u: raw U value
> + * @raw_v: raw V value
> + * @pixel: output pixel structure
> + *
> + * Converts raw Y, U, V component values to a normalized igt_pixel_t structure.
> + * For NV12 (8-bit), normalizes by 255. For P010 (10-bit in upper bits),
> + * shifts and normalizes by 1023.
> + *
> + * Result: pixel->r = normalized Y, pixel->g = normalized U, pixel->b = normalized V
> + */
> +static void
> +igt_color_yuv_to_pixel(uint32_t drm_format, uint32_t raw_y, uint32_t raw_u,
> +		       uint32_t raw_v, igt_pixel_t *pixel)
> +{
> +	if (drm_format == DRM_FORMAT_NV12) {
> +		/* Normalize 8-bit values to [0.0, 1.0] */
> +		pixel->r = raw_y / 255.0f;
> +		pixel->g = raw_u / 255.0f;
> +		pixel->b = raw_v / 255.0f;
> +	} else if (drm_format == DRM_FORMAT_P010) {
> +		/* P010 uses upper 10 bits of 16-bit value */
> +		pixel->r = (raw_y >> 6) / 1023.0f;
> +		pixel->g = (raw_u >> 6) / 1023.0f;
> +		pixel->b = (raw_v >> 6) / 1023.0f;
> +	} else {
> +		igt_skip("YUV pixel format support not implemented");
> +	}
> +}
> +
>   static int
>   igt_get_lut3d_index_blue_fast(int r, int g, int b, long dim, int components)
>   {