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    Subject[PATCH v6 08/17] drm/vkms: Avoid computing blending limits inside pre_mul_alpha_blend
    The pre_mul_alpha_blend is dedicated to blending, so to avoid mixing
    different concepts (coordinate calculation and color management), extract
    the x_limit and x_dst computation outside of this helper.
    It also increases the maintainability by grouping the computation related
    to coordinates in the same place: the loop in `blend`.

    Signed-off-by: Louis Chauvet <louis.chauvet@bootlin.com>
    ---
    drivers/gpu/drm/vkms/vkms_composer.c | 40 +++++++++++++++++-------------------
    1 file changed, 19 insertions(+), 21 deletions(-)

    diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
    index da0651a94c9b..45b111c74884 100644
    --- a/drivers/gpu/drm/vkms/vkms_composer.c
    +++ b/drivers/gpu/drm/vkms/vkms_composer.c
    @@ -24,34 +24,30 @@ static u16 pre_mul_blend_channel(u16 src, u16 dst, u16 alpha)

    /**
    * pre_mul_alpha_blend - alpha blending equation
    - * @frame_info: Source framebuffer's metadata
    * @stage_buffer: The line with the pixels from src_plane
    * @output_buffer: A line buffer that receives all the blends output
    + * @x_start: The start offset
    + * @pixel_count: The number of pixels to blend
    *
    - * Using the information from the `frame_info`, this blends only the
    - * necessary pixels from the `stage_buffer` to the `output_buffer`
    - * using premultiplied blend formula.
    + * The pixels 0..@pixel_count in stage_buffer are blended at @x_start..@x_start+@pixel_count in
    + * output_buffer.
    *
    * The current DRM assumption is that pixel color values have been already
    * pre-multiplied with the alpha channel values. See more
    * drm_plane_create_blend_mode_property(). Also, this formula assumes a
    * completely opaque background.
    */
    -static void pre_mul_alpha_blend(struct vkms_frame_info *frame_info,
    - struct line_buffer *stage_buffer,
    - struct line_buffer *output_buffer)
    +static void pre_mul_alpha_blend(const struct line_buffer *stage_buffer,
    + struct line_buffer *output_buffer, int x_start, int pixel_count)
    {
    - int x_dst = frame_info->dst.x1;
    - struct pixel_argb_u16 *out = output_buffer->pixels + x_dst;
    - struct pixel_argb_u16 *in = stage_buffer->pixels;
    - int x_limit = min_t(size_t, drm_rect_width(&frame_info->dst),
    - stage_buffer->n_pixels);
    -
    - for (int x = 0; x < x_limit; x++) {
    - out[x].a = (u16)0xffff;
    - out[x].r = pre_mul_blend_channel(in[x].r, out[x].r, in[x].a);
    - out[x].g = pre_mul_blend_channel(in[x].g, out[x].g, in[x].a);
    - out[x].b = pre_mul_blend_channel(in[x].b, out[x].b, in[x].a);
    + struct pixel_argb_u16 *out = &output_buffer->pixels[x_start];
    + const struct pixel_argb_u16 *in = stage_buffer->pixels;
    +
    + for (int i = 0; i < pixel_count; i++) {
    + out[i].a = (u16)0xffff;
    + out[i].r = pre_mul_blend_channel(in[i].r, out[i].r, in[i].a);
    + out[i].g = pre_mul_blend_channel(in[i].g, out[i].g, in[i].a);
    + out[i].b = pre_mul_blend_channel(in[i].b, out[i].b, in[i].a);
    }
    }

    @@ -183,7 +179,7 @@ static void blend(struct vkms_writeback_job *wb,
    {
    struct vkms_plane_state **plane = crtc_state->active_planes;
    u32 n_active_planes = crtc_state->num_active_planes;
    - int y_pos;
    + int y_pos, x_dst, pixel_count;

    const struct pixel_argb_u16 background_color = { .a = 0xffff };

    @@ -201,14 +197,16 @@ static void blend(struct vkms_writeback_job *wb,

    /* The active planes are composed associatively in z-order. */
    for (size_t i = 0; i < n_active_planes; i++) {
    + x_dst = plane[i]->frame_info->dst.x1;
    + pixel_count = min_t(int, drm_rect_width(&plane[i]->frame_info->dst),
    + (int)stage_buffer->n_pixels);
    y_pos = get_y_pos(plane[i]->frame_info, y);

    if (!check_limit(plane[i]->frame_info, y_pos))
    continue;

    vkms_compose_row(stage_buffer, plane[i], y_pos);
    - pre_mul_alpha_blend(plane[i]->frame_info, stage_buffer,
    - output_buffer);
    + pre_mul_alpha_blend(stage_buffer, output_buffer, x_dst, pixel_count);
    }

    apply_lut(crtc_state, output_buffer);
    --
    2.43.0


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