Re-add MipFilter::kBase, but keep kNearest as the default.

impeller/core/formats.h

@@ -9,7 +9,6 @@
 #include <functional>
 #include <memory>
 #include <string>
-#include <type_traits>
 
 #include "flutter/fml/hash_combine.h"
 #include "flutter/fml/logging.h"
@@ -404,19 +403,32 @@ struct Viewport {
   }
 };
 
+/// @brief      Describes how the texture should be sampled when the texture
+///             is being shrunk (minified) or expanded (magnified) to fit to
+///             the sample point.
 enum class MinMagFilter {
   /// Select nearest to the sample point. Most widely supported.
   kNearest,
+
   /// Select two points and linearly interpolate between them. Some formats
   /// may not support this.
   kLinear,
 };
 
+/// @brief      Options for selecting and filtering between mipmap levels.
 enum class MipFilter {
-  /// Sample from the nearest mip level.
+  /// @brief    The texture is sampled as if it only had a single mipmap level.
+  ///
+  ///           All samples are read from level 0.
+  kBase,
+
+  /// @brief    The nearst mipmap level is selected.
   kNearest,
-  /// Sample from the two nearest mip levels and linearly interpolate between
-  /// them.
+
+  /// @brief    Sample from the two nearest mip levels and linearly interpolate.
+  ///
+  ///           If the filter falls between levels, both levels are sampled, and
+  ///           their results linearly interpolated between levels.
   kLinear,
 };
 

impeller/core/sampler_descriptor.h

@@ -15,6 +15,11 @@ class Context;
 struct SamplerDescriptor final : public Comparable<SamplerDescriptor> {
   MinMagFilter min_filter = MinMagFilter::kNearest;
   MinMagFilter mag_filter = MinMagFilter::kNearest;
+
+  // TODO(https://github.com/flutter/flutter/issues/148253):
+  // `MipFilter::kNearest` is the default value for mip filters, as it
+  // cooresponds with the framework's `FilterQuality.low`. If we ever change the
+  // default filter quality, we should update this function to match.
   MipFilter mip_filter = MipFilter::kNearest;
 
   SamplerAddressMode width_address_mode = SamplerAddressMode::kClampToEdge;

impeller/display_list/dl_dispatcher.cc

@@ -119,6 +119,7 @@ static impeller::SamplerDescriptor ToSamplerDescriptor(
   switch (options) {
     case flutter::DlImageSampling::kNearestNeighbor:
       desc.min_filter = desc.mag_filter = impeller::MinMagFilter::kNearest;
+      desc.mip_filter = impeller::MipFilter::kBase;
       desc.label = "Nearest Sampler";
       break;
     case flutter::DlImageSampling::kLinear:

impeller/entity/contents/text_contents.cc

@@ -125,7 +125,9 @@ bool TextContents::Render(const ContentContext& renderer,
     sampler_desc.min_filter = MinMagFilter::kLinear;
     sampler_desc.mag_filter = MinMagFilter::kLinear;
   }
-  sampler_desc.mip_filter = MipFilter::kNearest;
+
+  // No mipmaps for glyph atlas (glyphs are generated at exact scales).
+  sampler_desc.mip_filter = MipFilter::kBase;
 
   FS::BindGlyphAtlasSampler(
       pass,                 // command

impeller/renderer/backend/gles/sampler_gles.cc

@@ -16,19 +16,20 @@ SamplerGLES::SamplerGLES(SamplerDescriptor desc) : Sampler(std::move(desc)) {}
 
 SamplerGLES::~SamplerGLES() = default;
 
-static GLint ToParam(MinMagFilter minmag_filter,
-                     std::optional<MipFilter> mip_filter = std::nullopt) {
-  if (!mip_filter.has_value()) {
-    switch (minmag_filter) {
-      case MinMagFilter::kNearest:
-        return GL_NEAREST;
-      case MinMagFilter::kLinear:
-        return GL_LINEAR;
-    }
-    FML_UNREACHABLE();
+static GLint ToParam(MinMagFilter minmag_filter) {
+  switch (minmag_filter) {
+    case MinMagFilter::kNearest:
+      return GL_NEAREST;
+    case MinMagFilter::kLinear:
+      return GL_LINEAR;
   }
+  FML_UNREACHABLE();
+}
 
-  switch (mip_filter.value()) {
+static GLint ToParam(MinMagFilter minmag_filter, MipFilter mip_filter) {
+  switch (mip_filter) {
+    case MipFilter::kBase:
+      return ToParam(minmag_filter);
     case MipFilter::kNearest:
       switch (minmag_filter) {
         case MinMagFilter::kNearest:
@@ -82,14 +83,18 @@ bool SamplerGLES::ConfigureBoundTexture(const TextureGLES& texture,
   }
   const auto& desc = GetDescriptor();
 
-  std::optional<MipFilter> mip_filter = std::nullopt;
+  GLint mag_filter = ToParam(desc.mag_filter);
+
+  // If the texture doesn't have mipmaps, we can't use mip filtering.
+  GLint min_filter;
   if (texture.GetTextureDescriptor().mip_count > 1) {
-    mip_filter = desc.mip_filter;
+    min_filter = ToParam(desc.min_filter, desc.mip_filter);
+  } else {
+    min_filter = ToParam(desc.min_filter);
   }
 
-  gl.TexParameteri(*target, GL_TEXTURE_MIN_FILTER,
-                   ToParam(desc.min_filter, mip_filter));
-  gl.TexParameteri(*target, GL_TEXTURE_MAG_FILTER, ToParam(desc.mag_filter));
+  gl.TexParameteri(*target, GL_TEXTURE_MIN_FILTER, min_filter);
+  gl.TexParameteri(*target, GL_TEXTURE_MAG_FILTER, mag_filter);
 
   const auto supports_decal_mode =
       gl.GetCapabilities()->SupportsDecalSamplerAddressMode();

impeller/renderer/backend/metal/formats_mtl.h

@@ -342,6 +342,8 @@ constexpr MTLSamplerMinMagFilter ToMTLSamplerMinMagFilter(MinMagFilter filter) {
 
 constexpr MTLSamplerMipFilter ToMTLSamplerMipFilter(MipFilter filter) {
   switch (filter) {
+    case MipFilter::kBase:
+      return MTLSamplerMipFilterNotMipmapped;
     case MipFilter::kNearest:
       return MTLSamplerMipFilterNearest;
     case MipFilter::kLinear:

impeller/renderer/backend/vulkan/formats_vk.h

@@ -222,6 +222,7 @@ constexpr vk::Filter ToVKSamplerMinMagFilter(MinMagFilter filter) {
 
 constexpr vk::SamplerMipmapMode ToVKSamplerMipmapMode(MipFilter filter) {
   switch (filter) {
+    case MipFilter::kBase:
     case MipFilter::kNearest:
       return vk::SamplerMipmapMode::eNearest;
     case MipFilter::kLinear:

impeller/renderer/backend/vulkan/sampler_vk.cc

@@ -7,15 +7,14 @@
 #include "impeller/renderer/backend/vulkan/context_vk.h"
 #include "impeller/renderer/backend/vulkan/formats_vk.h"
 #include "impeller/renderer/backend/vulkan/yuv_conversion_vk.h"
+#include "vulkan/vulkan_core.h"
 
 namespace impeller {
 
 static vk::UniqueSampler CreateSampler(
     const vk::Device& device,
     const SamplerDescriptor& desc,
     const std::shared_ptr<YUVConversionVK>& yuv_conversion) {
-  const auto mip_map = ToVKSamplerMipmapMode(desc.mip_filter);
-
   const auto min_filter = ToVKSamplerMinMagFilter(desc.min_filter);
   const auto mag_filter = ToVKSamplerMinMagFilter(desc.mag_filter);
 
@@ -36,9 +35,22 @@ static vk::UniqueSampler CreateSampler(
   sampler_info.addressModeV = address_mode_v;
   sampler_info.addressModeW = address_mode_w;
   sampler_info.borderColor = vk::BorderColor::eFloatTransparentBlack;
-  sampler_info.mipmapMode = mip_map;
   sampler_info.maxLod = VK_LOD_CLAMP_NONE;
 
+  // https://registry.khronos.org/vulkan/specs/1.3-extensions/man/html/VkSamplerCreateInfo.html#_description
+  switch (desc.mip_filter) {
+    case MipFilter::kBase:
+      sampler_info.mipmapMode = vk::SamplerMipmapMode::eNearest;
+      sampler_info.minLod = sampler_info.maxLod = 0.0f;
+      break;
+    case MipFilter::kNearest:
+      sampler_info.mipmapMode = vk::SamplerMipmapMode::eNearest;
+      break;
+    case MipFilter::kLinear:
+      sampler_info.mipmapMode = vk::SamplerMipmapMode::eLinear;
+      break;
+  }
+
   if (yuv_conversion && yuv_conversion->IsValid()) {
     sampler_chain.get<vk::SamplerYcbcrConversionInfo>().conversion =
         yuv_conversion->GetConversion();

impeller/renderer/renderer_unittests.cc

@@ -781,8 +781,9 @@ TEST_P(RendererTest, CanGenerateMipmaps) {
   bool first_frame = true;
   auto host_buffer = HostBuffer::Create(context->GetResourceAllocator());
   Renderer::RenderCallback callback = [&](RenderTarget& render_target) {
-    const char* mip_filter_names[] = {"Nearest", "Linear"};
-    const MipFilter mip_filters[] = {MipFilter::kNearest, MipFilter::kLinear};
+    const char* mip_filter_names[] = {"Base", "Nearest", "Linear"};
+    const MipFilter mip_filters[] = {MipFilter::kBase, MipFilter::kNearest,
+                                     MipFilter::kLinear};
     const char* min_filter_names[] = {"Nearest", "Linear"};
     const MinMagFilter min_filters[] = {MinMagFilter::kNearest,
                                         MinMagFilter::kLinear};