Add subpixel offset to Viewer app.

This adds a two dimensional location dragger to drag the origin across a
pixel. Also makes the perspective dragger hidden when perspective is
off. Also adds 'Z' to toggle the zoom window mouse follow.

Change-Id: Ic75d16c95848b392608770c8ed0d4db23733242f
Reviewed-on: https://skia-review.googlesource.com/137701
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>

2 files changed, 55 insertions, 8 deletions

diff --git a/tools/viewer/Viewer.cpp b/tools/viewer/Viewer.cpp
index c9014fd77d..3675cc4fe2 100644
--- a/tools/viewer/Viewer.cpp
+++ b/tools/viewer/Viewer.cpp
@@ -177,6 +177,8 @@ Viewer::Viewer(int argc, char** argv, void* platformData)
     , fShowSlidePicker(false)
     , fShowImGuiTestWindow(false)
     , fShowZoomWindow(false)
+    , fZoomWindowFixed(false)
+    , fZoomWindowLocation{0.0f, 0.0f}
     , fLastImage(nullptr)
     , fBackendType(sk_app::Window::kNativeGL_BackendType)
     , fColorMode(ColorMode::kLegacy)
@@ -185,6 +187,7 @@ Viewer::Viewer(int argc, char** argv, void* platformData)
     , fColorSpaceTransferFn(g2Dot2_TransferFn)
     , fZoomLevel(0.0f)
     , fRotation(0.0f)
+    , fOffset{0.0f, 0.0f}
     , fGestureDevice(GestureDevice::kNone)
     , fPerspectiveMode(kPerspective_Off)
     , fTileCnt(0)
@@ -264,6 +267,10 @@ Viewer::Viewer(int argc, char** argv, void* platformData)
         this->fShowZoomWindow = !this->fShowZoomWindow;
         fWindow->inval();
     });
+    fCommands.addCommand('Z', "GUI", "Toggle zoom window state", [this]() {
+        this->fZoomWindowFixed = !this->fZoomWindowFixed;
+        fWindow->inval();
+    });
     fCommands.addCommand('s', "Overlays", "Toggle stats display", [this]() {
         fStatsLayer.setActive(!fStatsLayer.getActive());
         fWindow->inval();
@@ -942,6 +949,7 @@ SkMatrix Viewer::computePreTouchMatrix() {
     SkMatrix m = fDefaultMatrix;
     SkScalar zoomScale = (fZoomLevel < 0) ? SK_Scalar1 / (SK_Scalar1 - fZoomLevel)
                                           : SK_Scalar1 + fZoomLevel;
+    m.preTranslate(fOffset.x(), fOffset.y());
     m.preScale(zoomScale, zoomScale);
 
     const SkISize slideSize = fSlides[fCurrentSlide]->getDimensions();
@@ -1351,6 +1359,28 @@ static ImVec2 ImGui_DragPoint(const char* label, SkPoint* p,
     return ImVec2(pos.x + p->fX * size.x, pos.y + p->fY * size.y);
 }
 
+static bool ImGui_DragLocation(SkPoint* pt) {
+    ImDrawList* drawList = ImGui::GetWindowDrawList();
+
+    // Fit our image/canvas to the available width, and scale the height to maintain aspect ratio.
+    float canvasWidth = SkTMax(ImGui::GetContentRegionAvailWidth(), 50.0f);
+    ImVec2 size = ImVec2(canvasWidth, canvasWidth);
+    ImVec2 pos = ImGui::GetCursorScreenPos();
+
+    // Background rectangle
+    drawList->AddRectFilled(pos, ImVec2(pos.x + size.x, pos.y + size.y), IM_COL32(0, 0, 0, 128));
+
+    // Location marker
+    bool dragging = false;
+    ImVec2 tl = ImGui_DragPoint("SL", pt + 0, pos, size, &dragging);
+    drawList->AddCircle(tl, 5.0f, 0xFFFFFFFF);
+
+    ImGui::SetCursorScreenPos(ImVec2(pos.x, pos.y + size.y));
+    ImGui::Spacing();
+
+    return dragging;
+}
+
 static bool ImGui_DragQuad(SkPoint* pts) {
     ImDrawList* drawList = ImGui::GetWindowDrawList();
 
@@ -1519,14 +1549,21 @@ void Viewer::drawImGui() {
                     this->preTouchMatrixChanged();
                     paramsChanged = true;
                 }
+                if (ImGui::CollapsingHeader("Subpixel offset", ImGuiTreeNodeFlags_NoTreePushOnOpen)) {
+                    if (ImGui_DragLocation(&fOffset)) {
+                        this->preTouchMatrixChanged();
+                        paramsChanged = true;
+                    }
+                }
                 int perspectiveMode = static_cast<int>(fPerspectiveMode);
                 if (ImGui::Combo("Perspective", &perspectiveMode, "Off\0Real\0Fake\0\0")) {
                     fPerspectiveMode = static_cast<PerspectiveMode>(perspectiveMode);
                     this->preTouchMatrixChanged();
-                    this->updateTitle();
+                    paramsChanged = true;
                 }
-                if (ImGui_DragQuad(fPerspectivePoints)) {
+                if (perspectiveMode != kPerspective_Off && ImGui_DragQuad(fPerspectivePoints)) {
                     this->preTouchMatrixChanged();
+                    paramsChanged = true;
                 }
             }
 
@@ -1800,15 +1837,22 @@ void Viewer::drawImGui() {
                 zoomFactor = SkTMin(zoomFactor * 2, 32);
             }
 
-            ImVec2 mousePos = ImGui::GetMousePos();
+            if (!fZoomWindowFixed) {
+                ImVec2 mousePos = ImGui::GetMousePos();
+                fZoomWindowLocation = SkPoint::Make(mousePos.x, mousePos.y);
+            }
+            SkScalar x = fZoomWindowLocation.x();
+            SkScalar y = fZoomWindowLocation.y();
+            int xInt = SkScalarRoundToInt(x);
+            int yInt = SkScalarRoundToInt(y);
             ImVec2 avail = ImGui::GetContentRegionAvail();
 
             uint32_t pixel = 0;
             SkImageInfo info = SkImageInfo::MakeN32Premul(1, 1);
-            if (fLastImage->readPixels(info, &pixel, info.minRowBytes(), mousePos.x, mousePos.y)) {
+            if (fLastImage->readPixels(info, &pixel, info.minRowBytes(), xInt, yInt)) {
                 ImGui::SameLine();
                 ImGui::Text("(X, Y): %d, %d RGBA: %x %x %x %x",
-                            sk_float_round2int(mousePos.x), sk_float_round2int(mousePos.y),
+                            xInt, yInt,
                             SkGetPackedR32(pixel), SkGetPackedG32(pixel),
                             SkGetPackedB32(pixel), SkGetPackedA32(pixel));
             }
@@ -1817,13 +1861,13 @@ void Viewer::drawImGui() {
                 // Translate so the region of the image that's under the mouse cursor is centered
                 // in the zoom canvas:
                 c->scale(zoomFactor, zoomFactor);
-                c->translate(avail.x * 0.5f / zoomFactor - mousePos.x - 0.5f,
-                             avail.y * 0.5f / zoomFactor - mousePos.y - 0.5f);
+                c->translate(avail.x * 0.5f / zoomFactor - x - 0.5f,
+                             avail.y * 0.5f / zoomFactor - y - 0.5f);
                 c->drawImage(this->fLastImage, 0, 0);
 
                 SkPaint outline;
                 outline.setStyle(SkPaint::kStroke_Style);
-                c->drawRect(SkRect::MakeXYWH(mousePos.x, mousePos.y, 1, 1), outline);
+                c->drawRect(SkRect::MakeXYWH(x, y, 1, 1), outline);
             });
         }
 
diff --git a/tools/viewer/Viewer.h b/tools/viewer/Viewer.h
index 653548d9be..6fdcd36675 100644
--- a/tools/viewer/Viewer.h
+++ b/tools/viewer/Viewer.h
@@ -132,6 +132,8 @@ private:
     bool                   fShowImGuiTestWindow;
 
     bool                   fShowZoomWindow;
+    bool                   fZoomWindowFixed;
+    SkPoint                fZoomWindowLocation;
     sk_sp<SkImage>         fLastImage;
 
     sk_app::Window::BackendType fBackendType;
@@ -144,6 +146,7 @@ private:
     // transform data
     SkScalar               fZoomLevel;
     SkScalar               fRotation;
+    SkVector               fOffset;
 
     sk_app::CommandSet     fCommands;