Shaders: pack Phong light offset and count into 16 bits each.

To make room for two more 16-bit skinning-related values in the
PhongDrawUniform -- joint offset for multidraw and per-instance joint
count for instancing.

Originally I made those full 32 bits because I wanted to provide an
option to have a 64-bit light mask there instead of an offset + count.
But the mask is not really driver-friendly as going over the bits and
skipping zeros was behaving like if each pixel was affected by 64 lights
-- an absolute perf nightmare. I might reconsider this again later, but
for now that doesn't seem to make sense, and I need to put the
skinning-related info somewhere without inflating the per-draw uniform
by another 16-byte vector.

src/Magnum/Shaders/Phong.frag

@@ -183,11 +183,10 @@ uniform highp uint drawOffset
 struct DrawUniform {
     /* Can't be a mat3 because of ANGLE, see Phong.vert for details */
     mediump mat3x4 normalMatrix;
-    highp uvec4 materialIdReservedObjectIdLightOffsetLightCount;
+    highp uvec4 materialIdReservedObjectIdLightOffsetLightCountReserved;
-    #define draw_materialIdReserved materialIdReservedObjectIdLightOffsetLightCount.x
+    #define draw_materialIdReserved materialIdReservedObjectIdLightOffsetLightCountReserved.x
-    #define draw_objectId materialIdReservedObjectIdLightOffsetLightCount.y
+    #define draw_objectId materialIdReservedObjectIdLightOffsetLightCountReserved.y
-    #define draw_lightOffset materialIdReservedObjectIdLightOffsetLightCount.z
+    #define draw_lightOffsetLightCount materialIdReservedObjectIdLightOffsetLightCountReserved.z
-    #define draw_lightCount materialIdReservedObjectIdLightOffsetLightCount.w
 };
 
 layout(std140
@@ -382,7 +381,10 @@ void main() {
     lowp const float alphaMask = materials[materialId].material_alphaMask;
     #endif
     #if LIGHT_COUNT
-    mediump const uint lightOffset = draws[drawId].draw_lightOffset;
+    mediump const uint lightOffset = draws[drawId].draw_lightOffsetLightCount & 0xffffu;
+    #ifdef LIGHT_CULLING
+    mediump const uint lightCount = draws[drawId].draw_lightOffsetLightCount >> 16 & 0xffffu;
+    #endif
     #endif
     #endif
 
@@ -444,7 +446,7 @@ void main() {
     #ifndef LIGHT_CULLING
     for(int i = 0; i < LIGHT_COUNT; ++i)
     #else
-    for(uint i = 0u, actualLightCount = min(uint(LIGHT_COUNT), draws[drawId].draw_lightCount); i < actualLightCount; ++i)
+    for(uint i = 0u, actualLightCount = min(uint(LIGHT_COUNT), lightCount); i < actualLightCount; ++i)
     #endif
     {
         lowp const vec3 lightColor =

src/Magnum/Shaders/Phong.h

@@ -55,7 +55,13 @@ separate @ref PhongMaterialUniform structure, referenced by @ref materialId.
 */
 struct PhongDrawUniform {
     /** @brief Construct with default parameters */
-    constexpr explicit PhongDrawUniform(DefaultInitT = DefaultInit) noexcept: normalMatrix{Math::IdentityInit}, materialId{0}, objectId{0}, lightOffset{0}, lightCount{0xffffffffu} {}
+    constexpr explicit PhongDrawUniform(DefaultInitT = DefaultInit) noexcept: normalMatrix{Math::IdentityInit}, materialId{0}, objectId{0},
+        #ifndef CORRADE_TARGET_BIG_ENDIAN
+        lightOffset{0}, lightCount{0xffffu}
+        #else
+        lightCount{0xffffu}, lightOffset{0}
+        #endif
+        {}
 
     /** @brief Construct without initializing the contents */
     explicit PhongDrawUniform(NoInitT) noexcept: normalMatrix{NoInit} {}
@@ -168,7 +174,7 @@ struct PhongDrawUniform {
      */
     UnsignedInt objectId;
 
-    /**
+    /** @var lightOffset
      * @brief Light offset
      *
      * References the first light in the @ref PhongLightUniform array. Should
@@ -178,20 +184,34 @@ struct PhongDrawUniform {
      * Used only if @ref PhongGL::Flag::LightCulling is enabled, otherwise
      * light offset is implicitly @cpp 0 @ce.
      */
-    UnsignedInt lightOffset;
 
-    /**
+    /** @var lightCount
      * @brief Light count
      *
      * Specifies how many lights after the @p lightOffset are used from the
      * @ref PhongLightUniform array. Gets clamped by the shader so it's
      * together with @ref lightOffset not larger than the light count passed to
-     * @ref PhongGL constructor. Default value is @cpp 0xffffffffu @ce.
+     * @ref PhongGL constructor. Default value is @cpp 0xffffu @ce.
      *
      * Used only if @ref PhongGL::Flag::LightCulling is enabled, otherwise
      * light count is implicitly @ref PhongGL::lightCount().
      */
-    UnsignedInt lightCount;
+
+    /* This field is an UnsignedInt in the shader and lightOffset is extracted
+       as (value & 0xffff), so the order has to be different on BE */
+    #ifndef CORRADE_TARGET_BIG_ENDIAN
+    UnsignedShort lightOffset;
+    UnsignedShort lightCount;
+    #else
+    UnsignedShort lightCount;
+    UnsignedShort lightOffset;
+    #endif
+
+    /* warning: Member __pad1__ is not documented. FFS DOXYGEN WHY DO YOU THINK
+       I MADE THOSE UNNAMED, YOU DUMB FOOL */
+    #ifndef DOXYGEN_GENERATING_OUTPUT
+    Int:32;
+    #endif
 };
 
 /**

src/Magnum/Shaders/Phong.vert

@@ -132,11 +132,10 @@ struct DrawUniform {
        2. Forget to actually implement and test the damn thing.
     */
     mediump mat3x4 normalMatrix;
-    highp uvec4 materialIdReservedObjectIdLightOffsetLightCount;
+    highp uvec4 materialIdReservedObjectIdLightOffsetLightCountReserved;
-    #define draw_materialIdReserved materialIdReservedObjectIdLightOffsetLightCount.x
+    #define draw_materialIdReserved materialIdReservedObjectIdLightOffsetLightCountReserved.x
-    #define draw_objectId materialIdReservedObjectIdLightOffsetLightCount.y
+    #define draw_objectId materialIdReservedObjectIdLightOffsetLightCountReserved.y
-    #define draw_lightOffset materialIdReservedObjectIdLightOffsetLightCount.z
+    #define draw_lightOffsetLightCount materialIdReservedObjectIdLightOffsetLightCountReserved.z
-    #define draw_lightCount materialIdReservedObjectIdLightOffsetLightCount.w
 };
 
 layout(std140

src/Magnum/Shaders/Test/PhongTest.cpp

@@ -39,7 +39,7 @@ struct PhongTest: TestSuite::Tester {
     void drawUniformConstructDefault();
     void drawUniformConstructNoInit();
     void drawUniformSetters();
-    void drawUniformMaterialIdPacking();
+    void drawUniformPacking();
 
     void materialUniformConstructDefault();
     void materialUniformConstructNoInit();
@@ -58,7 +58,7 @@ PhongTest::PhongTest() {
               &PhongTest::drawUniformConstructDefault,
               &PhongTest::drawUniformConstructNoInit,
               &PhongTest::drawUniformSetters,
-              &PhongTest::drawUniformMaterialIdPacking,
+              &PhongTest::drawUniformPacking,
 
               &PhongTest::materialUniformConstructDefault,
               &PhongTest::materialUniformConstructNoInit,
@@ -115,8 +115,8 @@ void PhongTest::drawUniformConstructDefault() {
     CORRADE_COMPARE(b.objectId, 0);
     CORRADE_COMPARE(a.lightOffset, 0);
     CORRADE_COMPARE(b.lightOffset, 0);
-    CORRADE_COMPARE(a.lightCount, 0xffffffffu);
+    CORRADE_COMPARE(a.lightCount, 0xffffu);
-    CORRADE_COMPARE(b.lightCount, 0xffffffffu);
+    CORRADE_COMPARE(b.lightCount, 0xffffu);
 
     constexpr PhongDrawUniform ca;
     constexpr PhongDrawUniform cb{DefaultInit};
@@ -136,8 +136,8 @@ void PhongTest::drawUniformConstructDefault() {
     CORRADE_COMPARE(cb.objectId, 0);
     CORRADE_COMPARE(ca.lightOffset, 0);
     CORRADE_COMPARE(cb.lightOffset, 0);
-    CORRADE_COMPARE(ca.lightCount, 0xffffffffu);
+    CORRADE_COMPARE(ca.lightCount, 0xffffu);
-    CORRADE_COMPARE(cb.lightCount, 0xffffffffu);
+    CORRADE_COMPARE(cb.lightCount, 0xffffu);
 
     CORRADE_VERIFY(std::is_nothrow_default_constructible<PhongDrawUniform>::value);
     CORRADE_VERIFY(std::is_nothrow_constructible<PhongDrawUniform, DefaultInitT>::value);
@@ -189,12 +189,20 @@ void PhongTest::drawUniformSetters() {
     CORRADE_COMPARE(a.lightCount, 13);
 }
 
-void PhongTest::drawUniformMaterialIdPacking() {
+void PhongTest::drawUniformPacking() {
     PhongDrawUniform a;
-    a.setMaterialId(13765);
+    a.setMaterialId(13765)
+     /* second 16 bits unused */
+     .setLightOffsetCount(13766, 63573);
     /* The normalMatrix field is 3x4 floats, materialId should be right after
        in the low 16 bits on both LE and BE */
     CORRADE_COMPARE(reinterpret_cast<UnsignedInt*>(&a)[12] & 0xffff, 13765);
+    /* second 16 bits unused */
+
+    /* lightOffset should be in the low 16 bits on both LE and BE, lightCount
+       in the high */
+    CORRADE_COMPARE(reinterpret_cast<UnsignedInt*>(&a)[14] & 0xffff, 13766);
+    CORRADE_COMPARE((reinterpret_cast<UnsignedInt*>(&a)[14] >> 16) & 0xffff, 63573);
 }
 
 void PhongTest::materialUniformConstructDefault() {