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++ // Copyright (C) 2026 The Qt Company Ltd.
++ // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
++
++ // Checks that the augmented pass binds the right texture to each sampler it
++ // declares. The samplers come from Texture properties of the RenderPass, but
++ // only one of them resolves to a GPU texture; the others stay unbound and have
++ // to receive the engine's dummy texture, which is opaque black.
++ //
++ // Sampling the unbound ones is deliberate: it keeps the samplers live so they
++ // cannot be optimized out of the shader's resource list, and it fails the
++ // check if the dummy fill were ever to overwrite the bound texture instead.
++
++ void MAIN_FRAGMENT_AUGMENT()
++ {
++ // The source rectangles are a single flat colour, so a fixed coordinate is
++ // enough and this does not depend on the model's UVs.
++ vec4 fromBound = texture(boundMap, vec2(0.5));
++ vec4 fromUnbound = texture(unboundMap, vec2(0.5));
++
++ // The dummy cube map is uploaded face by face. Only +X used to be filled,
++ // leaving the rest undefined, so sample three of the other five. Requiring
++ // opaque black rather than just black is what catches an unwritten face:
++ // uninitialized memory reads back with a zero alpha far more often than
++ // with a one.
++ vec4 cubeNegX = texture(unboundCube, vec3(-1.0, 0.0, 0.0));
++ vec4 cubePosY = texture(unboundCube, vec3(0.0, 1.0, 0.0));
++ vec4 cubeNegZ = texture(unboundCube, vec3(0.0, 0.0, -1.0));
++
++ bool boundOk = fromBound.r < 0.25 && fromBound.g > 0.75 && fromBound.b < 0.25;
++ bool unboundOk = fromUnbound.r < 0.05 && fromUnbound.g < 0.05
++ && fromUnbound.b < 0.05 && fromUnbound.a > 0.95;
++ bool cubeOk = cubeNegX.r < 0.05 && cubeNegX.g < 0.05 && cubeNegX.b < 0.05 && cubeNegX.a > 0.95
++ && cubePosY.r < 0.05 && cubePosY.g < 0.05 && cubePosY.b < 0.05 && cubePosY.a > 0.95
++ && cubeNegZ.r < 0.05 && cubeNegZ.g < 0.05 && cubeNegZ.b < 0.05 && cubeNegZ.a > 0.95;
++
++ fragOutput = (boundOk && unboundOk && cubeOk) ? vec4(0.0, 1.0, 0.0, 1.0) : vec4(1.0, 0.0, 0.0, 1.0);
++ }