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vk_native: honour the premultiplied flag on window-space layers (#1786) #1787

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Merged
dfattal merged 2 commits into from
Oct 2, 2026
Merged

vk_native: honour the premultiplied flag on window-space layers (#1786) #1787

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603d422
vk_native: honour the premultiplied flag on window-space layers (#1786)
dfattal Oct 2, 2026
6b53582
tests: allow GL's window-space SOURCE_ALPHA_BIT read (#1786)
dfattal Oct 2, 2026
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33 changes: 32 additions & 1 deletion src/xrt/auxiliary/vk/vk_hud_blend.c
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Original file line number Diff line number Diff line change
Expand Up @@ -324,6 +324,16 @@ vk_hud_blend_init_ex(struct vk_hud_blend *blend,
return false;
}

// #1786: premultiplied variant, same state but colour src ONE. Picked per
// draw by vk_hud_blend_draw_no_layout_ex(); everything else uses the
// straight pipeline above.
blend_att.srcColorBlendFactor = VK_BLEND_FACTOR_ONE;
ret = vk->vkCreateGraphicsPipelines(vk->device, VK_NULL_HANDLE, 1, &pipe_ci, NULL, &blend->pipeline_premul);
if (ret != VK_SUCCESS) {
U_LOG_E("[HUD blend] Failed to create premultiplied pipeline: %d", ret);
return false;
}

blend->initialized = true;
return true;
}
Expand Down Expand Up @@ -527,6 +537,23 @@ vk_hud_blend_draw_no_layout(struct vk_hud_blend *blend,
int32_t dst_y,
uint32_t dst_w,
uint32_t dst_h)
{
vk_hud_blend_draw_no_layout_ex(blend, vk, cmd, fb, fb_w, fb_h, hud_image, dst_x, dst_y, dst_w, dst_h, false);
}

void
vk_hud_blend_draw_no_layout_ex(struct vk_hud_blend *blend,
struct vk_bundle *vk,
VkCommandBuffer cmd,
VkFramebuffer fb,
uint32_t fb_w,
uint32_t fb_h,
VkImage hud_image,
int32_t dst_x,
int32_t dst_y,
uint32_t dst_w,
uint32_t dst_h,
bool premultiplied)
{
if (!blend->initialized || hud_image == VK_NULL_HANDLE || fb == VK_NULL_HANDLE ||
dst_w == 0 || dst_h == 0) {
Expand All @@ -551,7 +578,8 @@ vk_hud_blend_draw_no_layout(struct vk_hud_blend *blend,
VkRect2D scissor = {{dst_x, dst_y}, {dst_w, dst_h}};
vk->vkCmdSetScissor(cmd, 0, 1, &scissor);

vk->vkCmdBindPipeline(cmd, VK_PIPELINE_BIND_POINT_GRAPHICS, blend->pipeline);
vk->vkCmdBindPipeline(cmd, VK_PIPELINE_BIND_POINT_GRAPHICS,
premultiplied ? blend->pipeline_premul : blend->pipeline);
vk->vkCmdBindDescriptorSets(cmd, VK_PIPELINE_BIND_POINT_GRAPHICS, blend->pipe_layout, 0, 1,
&desc_set, 0, NULL);
vk->vkCmdDraw(cmd, 3, 1, 0, 0);
Expand Down Expand Up @@ -598,6 +626,9 @@ vk_hud_blend_fini(struct vk_hud_blend *blend, struct vk_bundle *vk)
if (blend->pipeline != VK_NULL_HANDLE) {
vk->vkDestroyPipeline(vk->device, blend->pipeline, NULL);
}
if (blend->pipeline_premul != VK_NULL_HANDLE) {
vk->vkDestroyPipeline(vk->device, blend->pipeline_premul, NULL);
}
if (blend->render_pass != VK_NULL_HANDLE) {
vk->vkDestroyRenderPass(vk->device, blend->render_pass, NULL);
}
Expand Down
27 changes: 26 additions & 1 deletion src/xrt/auxiliary/vk/vk_hud_blend.h
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Original file line number Diff line number Diff line change
Expand Up @@ -45,7 +45,8 @@ extern "C" {
struct vk_hud_blend
{
VkRenderPass render_pass;
VkPipeline pipeline;
VkPipeline pipeline; //!< Straight-alpha colour blend (src SRC_ALPHA).
VkPipeline pipeline_premul; //!< Premultiplied colour blend (src ONE), #1786.
VkPipelineLayout pipe_layout;
VkDescriptorSetLayout desc_layout;
VkDescriptorPool desc_pool;
Expand Down Expand Up @@ -138,6 +139,30 @@ vk_hud_blend_draw(struct vk_hud_blend *blend,
uint32_t dst_w,
uint32_t dst_h);

/*!
* vk_hud_blend_draw_no_layout(), choosing the colour blend per draw (#1786).
*
* @p premultiplied false is the straight-alpha blend every other draw uses
* (colour src SRC_ALPHA, dst ONE_MINUS_SRC_ALPHA). True treats the source as
* premultiplied (colour src ONE, dst ONE_MINUS_SRC_ALPHA). The alpha blend is
* whatever the blend was initialized with, in both cases.
*
* @ingroup aux_vk
*/
void
vk_hud_blend_draw_no_layout_ex(struct vk_hud_blend *blend,
struct vk_bundle *vk,
VkCommandBuffer cmd,
VkFramebuffer fb,
uint32_t fb_w,
uint32_t fb_h,
VkImage hud_image,
int32_t dst_x,
int32_t dst_y,
uint32_t dst_w,
uint32_t dst_h,
bool premultiplied);

/*!
* Draw without managing target image layout transitions or framebuffer
* caching. Use this when blending into a non-swapchain target (e.g. an
Expand Down
6 changes: 5 additions & 1 deletion src/xrt/compositor/gl/comp_gl_compositor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6244,7 +6244,11 @@ gl_compositor_layer_commit_locked(struct xrt_compositor *xc, xrt_graphics_sync_h

glUseProgram(c->program_window_space);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
// #1786: same rule as D3D11/D3D12/vk_native's window-space pass —
// SOURCE_ALPHA_BIT clear means premultiplied bytes, set means
// straight. Deliberately not comp_layer_blend_mode() (#1599).
bool ws_premultiplied = (layer->data.flags & XRT_LAYER_COMPOSITION_BLEND_TEXTURE_SOURCE_ALPHA_BIT) == 0;
glBlendFunc(ws_premultiplied ? GL_ONE : GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

GLint loc_ws_rect = glGetUniformLocation(c->program_window_space, "u_rect");
GLint loc_ws_tex = glGetUniformLocation(c->program_window_space, "u_texture");
Expand Down
12 changes: 9 additions & 3 deletions src/xrt/compositor/vk_native/comp_vk_native_compositor.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2622,6 +2622,12 @@ vk_compositor_render_window_space_into_atlas(struct comp_vk_native_compositor *c
const struct xrt_layer_window_space_data *ws = &layer->data.window_space;
uint32_t sc_index = ws->sub.image_index;

// #1786: same rule as D3D11/D3D12's window-space pass —
// SOURCE_ALPHA_BIT clear means premultiplied bytes, set means
// straight. Deliberately not comp_layer_blend_mode() (#1599): see
// the comment in comp_d3d11_renderer.cpp's window-space draw.
bool ws_premultiplied = (layer->data.flags & XRT_LAYER_COMPOSITION_BLEND_TEXTURE_SOURCE_ALPHA_BIT) == 0;

VkImage src_image = (VkImage)(uintptr_t)
comp_vk_native_swapchain_get_image(xsc, sc_index);
if (src_image == VK_NULL_HANDLE) {
Expand Down Expand Up @@ -2699,9 +2705,9 @@ vk_compositor_render_window_space_into_atlas(struct comp_vk_native_compositor *c
}
}

vk_hud_blend_draw_no_layout(&c->window_space_blend, vk, cmd,
c->atlas_ws_fb, atlas_w, atlas_h,
src_image, dx, dy, (uint32_t)dw_i, (uint32_t)dh_i);
vk_hud_blend_draw_no_layout_ex(&c->window_space_blend, vk, cmd, c->atlas_ws_fb, atlas_w,
atlas_h, src_image, dx, dy, (uint32_t)dw_i, (uint32_t)dh_i,
ws_premultiplied);
}

// Source back to COLOR_ATTACHMENT_OPTIMAL so the app can rerender.
Expand Down
5 changes: 4 additions & 1 deletion tests/tests_comp_layer_view_camera.cpp
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Expand Up @@ -1134,7 +1134,10 @@ TEST_CASE("comp_layer_blend_mode: no backend reimplements the blend rule (#1621)
const char *rel;
uint32_t allowed_flag_reads;
} backends[] = {
{"gl/comp_gl_compositor.cpp", 0},
// #1786: GL's one allowance is the SAME Local2D / window-space
// channel D3D11's is (its own premul/straight decision, deliberately
// not comp_layer_blend_mode() -- see comp_d3d11_renderer.cpp).
{"gl/comp_gl_compositor.cpp", 1},
{"metal/comp_metal_compositor.m", 0},
// The Local2D / window-space channel, above.
{"d3d11/comp_d3d11_renderer.cpp", 1},
Expand Down
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