From 9764c13d6d2977903f407761b27d847c0056e1c4 Mon Sep 17 00:00:00 2001
From: ReinUsesLisp <reinuseslisp@airmail.cc>
Date: Wed, 30 Dec 2020 02:25:23 -0300
Subject: video_core: Rewrite the texture cache

The current texture cache has several points that hurt maintainability
and performance. It's easy to break unrelated parts of the cache
when doing minor changes. The cache can easily forget valuable
information about the cached textures by CPU writes or simply by its
normal usage.The current texture cache has several points that hurt
maintainability and performance. It's easy to break unrelated parts
of the cache when doing minor changes. The cache can easily forget
valuable information about the cached textures by CPU writes or simply
by its normal usage.

This commit aims to address those issues.
---
 src/video_core/texture_cache/decode_bc4.cpp | 97 +++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 src/video_core/texture_cache/decode_bc4.cpp

(limited to 'src/video_core/texture_cache/decode_bc4.cpp')

diff --git a/src/video_core/texture_cache/decode_bc4.cpp b/src/video_core/texture_cache/decode_bc4.cpp
new file mode 100644
index 000000000..017327975
--- /dev/null
+++ b/src/video_core/texture_cache/decode_bc4.cpp
@@ -0,0 +1,97 @@
+// Copyright 2020 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <algorithm>
+#include <array>
+#include <span>
+
+#include "common/assert.h"
+#include "common/common_types.h"
+#include "video_core/texture_cache/decode_bc4.h"
+#include "video_core/texture_cache/types.h"
+
+namespace VideoCommon {
+
+// https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_texture_compression_rgtc.txt
+[[nodiscard]] constexpr u32 DecompressBlock(u64 bits, u32 x, u32 y) {
+    const u32 code_offset = 16 + 3 * (4 * y + x);
+    const u32 code = (bits >> code_offset) & 7;
+    const u32 red0 = (bits >> 0) & 0xff;
+    const u32 red1 = (bits >> 8) & 0xff;
+    if (red0 > red1) {
+        switch (code) {
+        case 0:
+            return red0;
+        case 1:
+            return red1;
+        case 2:
+            return (6 * red0 + 1 * red1) / 7;
+        case 3:
+            return (5 * red0 + 2 * red1) / 7;
+        case 4:
+            return (4 * red0 + 3 * red1) / 7;
+        case 5:
+            return (3 * red0 + 4 * red1) / 7;
+        case 6:
+            return (2 * red0 + 5 * red1) / 7;
+        case 7:
+            return (1 * red0 + 6 * red1) / 7;
+        }
+    } else {
+        switch (code) {
+        case 0:
+            return red0;
+        case 1:
+            return red1;
+        case 2:
+            return (4 * red0 + 1 * red1) / 5;
+        case 3:
+            return (3 * red0 + 2 * red1) / 5;
+        case 4:
+            return (2 * red0 + 3 * red1) / 5;
+        case 5:
+            return (1 * red0 + 4 * red1) / 5;
+        case 6:
+            return 0;
+        case 7:
+            return 0xff;
+        }
+    }
+    return 0;
+}
+
+void DecompressBC4(std::span<const u8> input, Extent3D extent, std::span<u8> output) {
+    UNIMPLEMENTED_IF_MSG(extent.width % 4 != 0, "Unaligned width={}", extent.width);
+    UNIMPLEMENTED_IF_MSG(extent.height % 4 != 0, "Unaligned height={}", extent.height);
+    static constexpr u32 BLOCK_SIZE = 4;
+    size_t input_offset = 0;
+    for (u32 slice = 0; slice < extent.depth; ++slice) {
+        for (u32 block_y = 0; block_y < extent.height / 4; ++block_y) {
+            for (u32 block_x = 0; block_x < extent.width / 4; ++block_x) {
+                u64 bits;
+                std::memcpy(&bits, &input[input_offset], sizeof(bits));
+                input_offset += sizeof(bits);
+
+                for (u32 y = 0; y < BLOCK_SIZE; ++y) {
+                    for (u32 x = 0; x < BLOCK_SIZE; ++x) {
+                        const u32 linear_z = slice;
+                        const u32 linear_y = block_y * BLOCK_SIZE + y;
+                        const u32 linear_x = block_x * BLOCK_SIZE + x;
+                        const u32 offset_z = linear_z * extent.width * extent.height;
+                        const u32 offset_y = linear_y * extent.width;
+                        const u32 offset_x = linear_x;
+                        const u32 output_offset = (offset_z + offset_y + offset_x) * 4ULL;
+                        const u32 color = DecompressBlock(bits, x, y);
+                        output[output_offset + 0] = static_cast<u8>(color);
+                        output[output_offset + 1] = 0;
+                        output[output_offset + 2] = 0;
+                        output[output_offset + 3] = 0xff;
+                    }
+                }
+            }
+        }
+    }
+}
+
+} // namespace VideoCommon
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