Neither target API has GL_TEXTURE_RECTANGLE: ESSL has no rectangle sampler, and
Vulkan's SPIR-V environment does not allow Dim::Rect. Both emulate it on a plain 2D
texture, and the two differ in exactly one way - a rectangle lookup addresses texels
where a 2D one addresses [0,1].
That one difference now lives in one SPIR-V pass, so neither backend has to know about
it: every lookup taking normalized coordinates gets its coordinate divided by the size
the texture reports, and the image type is then rewritten to 2D. Magma had no rectangle
handling at all - it fed Dim::Rect straight to Vulkan, which read the texel coordinates
as normalized and sampled the edge, so all fifteen KHR-GL40.texture_gather.*-2drect
cases came back holding the clear colour.
This replaces the ESSL text rewrite that did the same divide for DirectGLES only. Doing
it in the module instead is both shorter and stricter: the pass resolves an operation's
image type through the sampled-image and pointer wrappers rather than matching a
sampler name in generated source, so it cannot be fooled by an expression where it
expected an identifier, and it needs no help from the frontend reflection to know which
samplers were rectangles.
Still declined, as before: the Dref *sample* forms, whose coordinate carries the compare
value in its last component, and the projective ones, where the divide would have to
happen after the perspective divide. texelFetch is deliberately untouched - integer
texel coordinates mean the same thing on both targets.
KHR-GL40.texture_gather: Magma 66 failures -> 2, Espryt stays at 75/75.
A rectangle texture is emulated on an ES 2D texture, and LowerRectImagesForEssl
rewrites the image type in the SPIR-V to match. That is exact only where the lookup
addresses texels directly, which is why the pass declined any module containing a
lookup that takes normalized coordinates - the whole KHR-GL40.texture_gather 2drect
set among them.
The missing half is one divide: a rectangle lookup's coordinate is in texels and the
2D lookup it becomes wants [0,1], so the coordinate has to be divided by the texture's
size. It goes in on the ESSL the transpiler produces, next to the LOD-bias emulation
that already rewrites lookup arguments there, and reads the size back with
textureSize() rather than plumbing a uniform down - the emulated texture is a real ES
2D texture, so the shader can ask it directly.
Only the forms whose argument 1 is the bare coordinate are rewritten - texture,
textureOffset and the three textureGather flavours, which covers the Dref gathers too
because those carry the compare value in a separate argument. texelFetch is
deliberately left alone: its coordinates are integer texels on both targets. The
SPIR-V pass keeps declining everything else, so a projective lookup or a Dref sample
(where the compare value rides in coord.z) still refuses the module instead of
producing something subtly wrong.
Which samplers were declared rectangle is no longer visible in the transpiled source -
they are plain sampler2D by then - so the names come from the frontend program's
reflection.
A three-channel format widened to four for a multisample target gains an alpha
channel the application never asked for, and it holds whatever the draw that filled
the texture happened to write there. GL says a format without alpha reads back as
1.0, so KHR-GL33.texture_swizzle - which fills such a texture by rendering
vec4(r, g, b, 0.0) and then swizzles red from alpha - read 0 where it expected the
maximum.
Fold ONE into the texture's swizzle for exactly those textures, composed with the
swizzle the application set, so the promotion stays invisible.
Legacy GLSL's gl_FragColor goes to every enabled draw buffer (GL 4.6 15.2.3),
but ShaderSourceProcessor lowers it to a single mg_FragColor output, which only
ever reaches draw buffer 0. Everything past the first attachment kept its
pre-draw contents.
Replicated across the enabled draw buffers with copies at the end of main.
Gated on the count so the ordinary single-target shader is byte-for-byte what it
was: the pass is a no-op below two draw buffers, and the count comes from the
frontend draw framebuffer at program-sync time (not from the backend framebuffer
sync, which only runs later in PrepareForDraw - a program compiled against a
stale count would not be relinked until the draw after the one that needed it).
It joins the snorm/unorm clamp masks as framebuffer state the shader is compiled
against, with the same relink-on-change check.
Also advertises GL_ARB_explicit_attrib_location and GL_ARB_texture_multisample,
which DirectGLES implements for every version it advertises but only listed for
DirectVulkan. Both are core from GL 3.2/3.3 on, so an app targeting 3.0/3.1
reaches them only through the extension string - without the former the CTS
picks an entirely different draw_buffers shader, and without the latter
KHR-GL31.texture_size_promotion.functional crashed outright.
KHR-GL3{0,1,2,3}.draw_buffers.draw_buffers_1 now passes on all four versions,
and texture_size_promotion.functional on GL31 downgrades from a crash to a
(still open) comparison failure.
ES has no per-texture or per-sampler LOD bias at all - GL_TEXTURE_LOD_BIAS is
desktop only, and Vulkan spells it VkSamplerCreateInfo::mipLodBias, which is why
DirectVulkan already honours it. DirectGLES stored the value in sampler state
and then dropped it, so every lookup sampled at the unbiased level of detail.
The bias now reaches the shader as a uniform: a new SPIRV-Cross post-pass
declares one `uniform highp float mg_lodBias_<sampler>;` per mip-capable sampler
and folds it into the level of detail of every lookup that has somewhere to put
it - appended as the bias argument, added to an existing bias, or added to an
explicit textureLod level (Vulkan applies mipLodBias to explicit-LOD fetches too,
and the CTS reference expects the same). texelFetch/textureGather have no bias
by definition, textureGrad offers no argument to fold one into, and the
array-shadow lookups have no bias overload in GLSL at all, so all of those are
left alone. Draws push the bound texture's (or the bound sampler object's, which
overrides it as in GL) value into the uniform, and only when it changed - a
shader whose samplers all have a zero bias issues no extra call at all.
Fixes KHR-GL3{0,2,3}.texture_lod_bias.texture_lod_bias_all.
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