gl/wg engines: zero size blur dropshadow support

- Implements support for zero size blur in drop shadow effects for both GL and WebGPU engines.
  When the blur sigma parameter is zero, the implementation now skips the blur processing entirely
  and uses the original image as the shadow source.  Improving performance and avoiding
  unnecessary computations

- EffectDropShadow example changed to reproduce zero sigma shadow

https://github.com/thorvg/thorvg/issues/3602

examples/EffectDropShadow.cpp

@@ -103,7 +103,7 @@ struct UserExample : tvgexam::Example
         scene2->push(tvg::SceneEffect::DropShadow, 65, 143, 222, (int)(255.0f * progress), 135.0, 10.0, 3.0, 100);
 
         scene3->push(tvg::SceneEffect::ClearAll);
-        scene3->push(tvg::SceneEffect::DropShadow, 0, 0, 0, 125, (double)(360.0f * progress), 20.0, 3.0, 100);
+        scene3->push(tvg::SceneEffect::DropShadow, 0, 0, 0, 125, (double)(360.0f * progress), 20.0, 0.0, 100);
 
         canvas->update();
 

src/renderer/gl_engine/tvgGlEffect.cpp

@@ -141,7 +141,7 @@ void GlEffect::update(RenderEffectDropShadow* effect, const Matrix& transform)
     dropShadow->offset[1] = offset.y;
     dropShadow->extend = 2 * std::max(sigma * scale + std::abs(offset.x), sigma * scale + std::abs(offset.y));
     effect->rd = dropShadow;
-    effect->valid = (dropShadow->extend > 0);
+    effect->valid = (dropShadow->extend >= 0);
 }
 
 

src/renderer/gl_engine/tvgGlRenderTask.cpp

@@ -544,6 +544,8 @@ void GlEffectDropShadowTask::run()
     GL_CHECK(glBlitFramebuffer(0, 0, width, height, 0, 0, width, height, GL_COLOR_BUFFER_BIT, GL_NEAREST));
     
     GL_CHECK(glDisable(GL_BLEND));
+    // when sigma is 0, no blur is applied, and the original image is used directly as the shadow.
+    if (!tvg::zero(effect->sigma)) {
         // horizontal blur
         GL_CHECK(glBindFramebuffer(GL_FRAMEBUFFER, mDstCopyFbo0->getResolveFboId()));
         horzTask->setViewport(vp);
@@ -558,6 +560,7 @@ void GlEffectDropShadowTask::run()
         GL_CHECK(glBindFramebuffer(GL_READ_FRAMEBUFFER, mDstFbo->getFboId()));
         GL_CHECK(glBindFramebuffer(GL_DRAW_FRAMEBUFFER, mDstCopyFbo0->getResolveFboId()));
         GL_CHECK(glBlitFramebuffer(0, 0, width, height, 0, 0, width, height, GL_COLOR_BUFFER_BIT, GL_NEAREST));
+    }
     // run drop shadow effect
     GL_CHECK(glBindFramebuffer(GL_FRAMEBUFFER, mDstFbo->getFboId()));
     GlRenderTask::run();

src/renderer/wg_engine/tvgWgCompositor.cpp

@@ -875,8 +875,9 @@ bool WgCompositor::dropShadow(WgContext& context, WgRenderTarget* dst, const Ren
     auto aabb = compose->aabb;
     auto viewport = compose->rdViewport;
 
-    { // apply blur
     copyTexture(&targetTemp1, dst, aabb);
+     // when sigma is 0, no blur is applied, and the original image is used directly as the shadow.
+    if (!tvg::zero(params->sigma)) {
         WgRenderTarget* sbuff = &targetTemp1;
         WgRenderTarget* dbuff = &targetTemp0;
         WGPUComputePassDescriptor computePassDesc{ .label = "Compute pass drop shadow blur" };

src/renderer/wg_engine/tvgWgRenderer.cpp

@@ -538,10 +538,10 @@ bool WgRenderer::region(RenderEffect* effect)
     } else if (effect->type == SceneEffect::DropShadow) {
         auto dropShadow = (RenderEffectDropShadow*)effect;
         auto renderData = (WgRenderDataEffectParams*)dropShadow->rd;
-        dropShadow->extend.min.x = -(renderData->extend + std::abs(renderData->offset.x));
+        dropShadow->extend.min.x = -std::ceil(renderData->extend + std::abs(renderData->offset.x));
-        dropShadow->extend.max.x = +(renderData->extend + std::abs(renderData->offset.x));
+        dropShadow->extend.min.y = -std::ceil(renderData->extend + std::abs(renderData->offset.y));
-        dropShadow->extend.min.y = -(renderData->extend + std::abs(renderData->offset.y));
+        dropShadow->extend.max.x = +std::floor(renderData->extend + std::abs(renderData->offset.x));
-        dropShadow->extend.max.y = +(renderData->extend + std::abs(renderData->offset.y));
+        dropShadow->extend.max.y = +std::floor(renderData->extend + std::abs(renderData->offset.y));
         return true;
     }
     return false;

src/renderer/wg_engine/tvgWgShaderTypes.cpp

@@ -247,7 +247,7 @@ bool WgShaderTypeEffectParams::update(RenderEffectDropShadow* dropShadow, const
     params[9] = offset.y;
     extend = params[2] * 2; // kernel
 
-    dropShadow->valid = (extend > 0);
+    dropShadow->valid = (extend >= 0);
     return dropShadow->valid;
 }