Fix GLSL translation of several Texture* operations (#800)

A user found that the `Texture2D<float2>.Load(...)` operation was not being compiled to GLSL properly, such that it returned a `vec4` instead of the expected `vec2`.

The GLSL texture-related functions always return (and take) 4-component vectors, and we already have infrastructure in `emit.cpp` for recognizing a `$z` operator in the GLSL intrinsic definition to stand in for an appropriate swizzle based on teh number of components in the texture result type.

This change just adds that `$z` operator to the GLSL code for several more texture operations (including `Load()`) that are defined on a `Texture*<T>` and that return `T`.

This change doesn't try to add additional GLSL translations for texture-related operations (e.g., additional variations like `SampleCmp` that we have defined in the stdlib but not given GLSL translations for). That work still needs to be done.

1 files changed, 21 insertions, 0 deletions

diff --git a/tests/cross-compile/texture-load.slang b/tests/cross-compile/texture-load.slang
new file mode 100644
index 000000000..71f22b13a
--- /dev/null
+++ b/tests/cross-compile/texture-load.slang
@@ -0,0 +1,21 @@
+// texture-load.slang
+
+// Confirm that texture `Load` operations yield the
+// expected type when compiled to SPIR-V.
+
+//TEST:CROSS_COMPILE:-target spirv-assembly -entry main -stage compute
+
+Texture2D<float2>   inputTexture;
+RWTexture2D<float2> outputTexture;
+
+cbuffer C
+{
+	int2 pos;
+}
+
+[numthreads(16, 16, 1)]
+void main(uint2 pixelIndex : SV_DispatchThreadID)
+{
+	float2 tmp = inputTexture.Load(int3(pos,0));
+    outputTexture[pos] = tmp;
+}