Buffer Conversions (#23)

* Why is this not working

* Revert helper shader changes for now

* Byte Index Buffer Restride

src/Ryujinx.Graphics.Metal/Shaders/ChangeBufferStride.metal

@@ -0,0 +1,52 @@
+#include <metal_stdlib>
+
+using namespace metal;
+
+kernel void kernelMain(constant int4& stride_arguments [[buffer(0)]],
+                       device uint8_t* in_data [[buffer(1)]],
+                       device uint8_t* out_data [[buffer(2)]],
+                       uint3 thread_position_in_grid [[thread_position_in_grid]],
+                       uint3 threads_per_threadgroup [[threads_per_threadgroup]],
+                       uint3 threadgroups_per_grid [[threads_per_grid]])
+{
+    // Determine what slice of the stride copies this invocation will perform.
+
+    int sourceStride = stride_arguments.x;
+    int targetStride = stride_arguments.y;
+    int bufferSize = stride_arguments.z;
+    int sourceOffset = stride_arguments.w;
+
+    int strideRemainder = targetStride - sourceStride;
+    int invocations = int(threads_per_threadgroup.x * threadgroups_per_grid.x);
+
+    int copiesRequired = bufferSize / sourceStride;
+
+    // Find the copies that this invocation should perform.
+
+    // - Copies that all invocations perform.
+    int allInvocationCopies = copiesRequired / invocations;
+
+    // - Extra remainder copy that this invocation performs.
+    int index = int(thread_position_in_grid.x);
+    int extra = (index < (copiesRequired % invocations)) ? 1 : 0;
+
+    int copyCount = allInvocationCopies + extra;
+
+    // Finally, get the starting offset. Make sure to count extra copies.
+
+    int startCopy = allInvocationCopies * index + min(copiesRequired % invocations, index);
+
+    int srcOffset = sourceOffset + startCopy * sourceStride;
+    int dstOffset = startCopy * targetStride;
+
+    // Perform the copies for this region
+    for (int i = 0; i < copyCount; i++) {
+        for (int j = 0; j < sourceStride; j++) {
+            out_data[dstOffset++] = in_data[srcOffset++];
+        }
+
+        for (int j = 0; j < strideRemainder; j++) {
+            out_data[dstOffset++] = uint8_t(0);
+        }
+    }
+}