Add polygon offset to the driver API

filament/src/driver/Driver.h

@@ -204,9 +204,15 @@ public:
         };
     };
 
+    struct PolygonOffset {
+        float slope = 0;        // factor in GL-speak
+        float constant = 0;     // units in GL-speak
+    };
+
     struct PipelineState {
         ProgramHandle program;
         RasterState rasterState;
+        PolygonOffset polygonOffset;
     };
 
     static SamplerFormat getSamplerFormat(TextureFormat format) noexcept;

filament/src/driver/opengl/OpenGLDriver.cpp

@@ -594,6 +594,26 @@ void OpenGLDriver::depthFunc(GLenum func) noexcept {
     });
 }
 
+void OpenGLDriver::polygonOffset(GLfloat factor, GLfloat units) noexcept {
+    // if we're in the shadow-pass, the default polygon offset is factor = unit = 1
+    // TODO: this should be controlled by filament, instead of being a feature of the driver
+    if (factor == 0 && units == 0) {
+        TargetBufferFlags clearFlags = (TargetBufferFlags)mRenderPassParams.clear;
+        if ((clearFlags & TargetBufferFlags::SHADOW) == TargetBufferFlags::SHADOW) {
+            factor = units = 1.0f;
+        }
+    }
+
+    update_state(state.polygonOffset, { factor, units }, [&]() {
+        if (factor != 0 || units != 0) {
+            glPolygonOffset(factor, units);
+            enable(GL_POLYGON_OFFSET_FILL);
+        } else {
+            disable(GL_POLYGON_OFFSET_FILL);
+        }
+    });
+}
+
 void OpenGLDriver::setRasterStateSlow(Driver::RasterState rs) noexcept {
     mRasterState = rs;
 
@@ -1975,12 +1995,6 @@ void OpenGLDriver::beginRenderPass(Driver::RenderTargetHandle rth,
     if (UTILS_UNLIKELY(state.draw_fbo != rt->gl.fbo)) {
         bindFramebuffer(GL_FRAMEBUFFER, rt->gl.fbo);
 
-        if ((clearFlags & TargetBufferFlags::SHADOW) == TargetBufferFlags::SHADOW) {
-            enable(GL_POLYGON_OFFSET_FILL);
-        } else {
-            disable(GL_POLYGON_OFFSET_FILL);
-        }
-
         // glInvalidateFramebuffer appeared on GLES 3.0 and GL4.3, for simplicity we just
         // ignore it on GL (rather than having to do a runtime check).
         if (GLES31_HEADERS && !bugs.disable_invalidate_framebuffer) {
@@ -2729,6 +2743,8 @@ void OpenGLDriver::draw(
 
     setRasterState(state.rasterState);
 
+    polygonOffset(state.polygonOffset.slope, state.polygonOffset.constant);
+
     glDrawRangeElements(GLenum(rp->type), rp->minIndex, rp->maxIndex, rp->count,
             rp->gl.indicesType, reinterpret_cast<const void*>(rp->offset));
 

filament/src/driver/opengl/OpenGLDriver.h

@@ -296,6 +296,7 @@ private:
             setRasterStateSlow(rs);
         }
     }
+
     void setTextureData(GLTexture* t,
             uint32_t level,
             uint32_t xoffset, uint32_t yoffset, uint32_t zoffset,
@@ -350,6 +351,7 @@ private:
     inline void colorMask(GLboolean flag) noexcept;
     inline void depthMask(GLboolean flag) noexcept;
     inline void depthFunc(GLenum func) noexcept;
+    inline void polygonOffset(GLfloat factor, GLfloat units) noexcept;
 
     inline void setScissor(GLint left, GLint bottom, GLsizei width, GLsizei height) noexcept;
     inline void setViewport(GLint left, GLint bottom, GLsizei width, GLsizei height) noexcept;
@@ -414,6 +416,14 @@ private:
             GLenum depthFunc            = GL_LESS;
         } raster;
 
+        struct PolygonOffset {
+            GLfloat factor = 0;
+            GLfloat units = 0;
+            bool operator != (PolygonOffset const& rhs) noexcept {
+                return factor != rhs.factor || units != rhs.units;
+            }
+        } polygonOffset;
+
         struct {
             utils::bitset32 caps;
         } enables;