GPU: Add scaling shader support

Currently only Bilinear (Sharp).

src/core/gpu_shadergen.cpp

@@ -0,0 +1,79 @@
+// SPDX-FileCopyrightText: 2019-2023 Connor McLaughlin <stenzek@gmail.com>
+// SPDX-License-Identifier: GPL-3.0
+
+#include "gpu_shadergen.h"
+
+GPUShaderGen::GPUShaderGen(RenderAPI render_api, bool supports_dual_source_blend)
+  : ShaderGen(render_api, supports_dual_source_blend)
+{
+}
+
+GPUShaderGen::~GPUShaderGen() = default;
+
+void GPUShaderGen::WriteDisplayUniformBuffer(std::stringstream& ss)
+{
+  DeclareUniformBuffer(ss, {"float4 u_src_rect", "float4 u_src_size", "float4 u_params"}, true);
+}
+
+std::string GPUShaderGen::GenerateDisplayVertexShader()
+{
+  std::stringstream ss;
+  WriteHeader(ss);
+  WriteDisplayUniformBuffer(ss);
+  DeclareVertexEntryPoint(ss, {}, 0, 1, {}, true);
+  ss << R"(
+{
+  float2 pos = float2(float((v_id << 1) & 2u), float(v_id & 2u));
+  v_tex0 = u_src_rect.xy + pos * u_src_rect.zw;
+  v_pos = float4(pos * float2(2.0f, -2.0f) + float2(-1.0f, 1.0f), 0.0f, 1.0f);
+  #if API_VULKAN
+    v_pos.y = -v_pos.y;
+  #endif
+}
+)";
+
+  return ss.str();
+}
+
+std::string GPUShaderGen::GenerateDisplayFragmentShader()
+{
+  std::stringstream ss;
+  WriteHeader(ss);
+  WriteDisplayUniformBuffer(ss);
+  DeclareTexture(ss, "samp0", 0);
+  DeclareFragmentEntryPoint(ss, 0, 1, {}, false, 1);
+  ss << R"(
+{
+  o_col0 = float4(SAMPLE_TEXTURE(samp0, v_tex0).rgb, 1.0f);
+})";
+
+  return ss.str();
+}
+
+std::string GPUShaderGen::GenerateDisplaySharpBilinearFragmentShader()
+{
+  std::stringstream ss;
+  WriteHeader(ss);
+  WriteDisplayUniformBuffer(ss);
+  DeclareTexture(ss, "samp0", 0, false);
+
+  // Based on https://github.com/rsn8887/Sharp-Bilinear-Shaders/blob/master/Copy_To_RetroPie/shaders/sharp-bilinear-simple.glsl
+  DeclareFragmentEntryPoint(ss, 0, 1, {}, false, 1, false, false, false, false);
+  ss << R"(
+{
+  float2 scale = u_params.xy;
+  float2 region_range = u_params.zw;
+
+  float2 texel = v_tex0 * u_src_size.xy;
+  float2 texel_floored = floor(texel);
+  float2 s = frac(texel);
+
+  float2 center_dist = s - 0.5;
+  float2 f = (center_dist - clamp(center_dist, -region_range, region_range)) * scale + 0.5;
+  float2 mod_texel = texel_floored + f;
+
+  o_col0 = float4(SAMPLE_TEXTURE(samp0, mod_texel * u_src_size.zw).rgb, 1.0f);
+})";
+
+  return ss.str();
+}