added cross dissolve transitions (but they're uneditable)

effects/crossdissolvetransition.cpp

@@ -0,0 +1,9 @@
+#include "transition.h"
+
+#include <QOpenGLFunctions>
+
+void CrossDissolveTransition::process_transition(float progress) {
+    float color[4];
+    glGetFloatv(GL_CURRENT_COLOR, color);
+    glColor4f(1.0, 1.0, 1.0, color[3]*progress);
+}

effects/transformeffect.cpp

@@ -205,5 +205,7 @@ void TransformEffect::process_gl(int* anchor_x, int* anchor_y) {
     }
 
 	// opacity
-	glColor4f(1.0, 1.0, 1.0, opacity->value()*0.01);
+    float color[4];
+    glGetFloatv(GL_CURRENT_COLOR, color);
+    glColor4f(1.0, 1.0, 1.0, color[3]*(opacity->value()*0.01));
 }

effects/transition.cpp

@@ -0,0 +1,7 @@
+#include "transition.h"
+
+Transition::Transition() {
+    length = 30;
+}
+
+void Transition::process_transition(float) {}

effects/transition.h

@@ -0,0 +1,17 @@
+#ifndef TRANSITION_H
+#define TRANSITION_H
+
+class Transition
+{
+public:
+    Transition();
+    int length;
+    virtual void process_transition(float);
+};
+
+class CrossDissolveTransition : public Transition {
+public:
+    void process_transition(float);
+};
+
+#endif // TRANSITION_H