tutorial: speed up texture uploads in the Mandelbrot viewer by only

sending the part we just modified.

test/tutorial/tut03.cpp

@@ -37,10 +37,14 @@ public:
     {
         m_size = size;
         m_pixels = new u8vec4[size.x * size.y];
-        m_frame = 0;
+        m_frame = -1;
         m_center = 0;
-        m_target = f64cmplx(0.001643721971153, 0.822467633298876);
+        //m_target = f64cmplx(0.001643721971153, 0.822467633298876);
+        m_target = f64cmplx(-1.207205434596, 0.315432814901);
+        //m_target = f64cmplx(-0.79192956889854, -0.14632423080102);
+        //m_target = f64cmplx(0.3245046418497685, 0.04855101129280834);
         //m_target = f64cmplx(0.28693186889504513, 0.014286693904085048);
+        m_angle = 0.0;
         m_radius = 8.0;
         m_ready = false;
     }
@@ -56,14 +60,17 @@ public:
 
         m_frame = (m_frame + 1) % 4;
 
-        double zoom = pow(2.0, -deltams * 0.00015);
+        double zoom = pow(2.0, -deltams * 0.0005);
         m_radius *= zoom;
         m_center = (m_center - m_target) * zoom * zoom + m_target;
 
         double step = m_radius / (m_size.x > m_size.y ? m_size.x : m_size.y);
+//        m_angle -= deltams * 0.00015;
+        f64cmplx transform = step * f64cmplx(cos(m_angle), sin(m_angle));
 
-        for (int j = m_frame / 2; j < m_size.y; j += 2)
-        //for (int j = ((m_frame + 1) % 4) / 2; j < m_size.y; j += 2)
+        u8vec4 *m_pixelstart = m_pixels + m_size.x * m_size.y / 4 * m_frame;
+
+        for (int j = ((m_frame + 1) % 4) / 2; j < m_size.y; j += 2)
         for (int i = m_frame % 2; i < m_size.x; i += 2)
         {
             double const maxlen = 32;
@@ -71,7 +78,7 @@ public:
 
             f64cmplx delta(i - m_size.x / 2, j - m_size.y / 2);
 
-            f64cmplx z0 = m_center + step * delta;
+            f64cmplx z0 = m_center + transform * delta;
             f64cmplx r0 = z0;
             //f64cmplx r0(0.28693186889504513, 0.014286693904085048);
             //f64cmplx r0(0.001643721971153, 0.822467633298876);
@@ -98,11 +105,11 @@ public:
                 uint8_t red = r * 255.0f;
                 uint8_t green = g * 255.0f;
                 uint8_t blue = b * 255.0f;
-                m_pixels[j * m_size.x + i] = u8vec4(red, green, blue, 0);
+                *m_pixelstart++ = u8vec4(red, green, blue, 0);
             }
             else
             {
-                m_pixels[j * m_size.x + i] = u8vec4(0, 0, 0, 0);
+                *m_pixelstart++ = u8vec4(0, 0, 0, 0);
             }
         }
     }
@@ -133,10 +140,12 @@ public:
 
         if (!m_ready)
         {
+            /* Create a texture of half the width and twice the height
+             * so that we can upload four different subimages each frame. */
             glGenTextures(1, &m_texid);
             glBindTexture(GL_TEXTURE_2D, m_texid);
-            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, m_size.x, m_size.y, 0,
-                         GL_RGBA, GL_UNSIGNED_BYTE, m_pixels);
+            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, m_size.x / 2, m_size.y * 2,
+                         0, GL_RGBA, GL_UNSIGNED_BYTE, m_pixels);
             glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
             glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
 
@@ -154,7 +163,16 @@ public:
                 "uniform sampler2D in_Texture;\n"
                 "void main(void) {"
                 "    vec2 coord = gl_TexCoord[0].xy;"
-                "    gl_FragColor = texture2D(in_Texture, coord);"
+                /* gl_FragCoord is centered inside the pixel, so we remove
+                 * 0.5 from gl_FragCoord.x. Also, (0,0) is at the bottom
+                 * left whereas our images have (0,0) at the top left, so we
+                 * _add_ 0.5 to gl_FragCoord.y. */
+                "    float i = mod(gl_FragCoord.x - 0.5, 2.0);"
+                "    float j = mod(gl_FragCoord.y + 0.5 + i, 2.0);"
+                "    coord.y += i + j * 2;"
+                "    coord.y *= 0.25;"
+                "    vec4 p = texture2D(in_Texture, coord);"
+                "    gl_FragColor = p;"
                 "}"
 #else
                 "void main(float4 in_Position : POSITION,"
@@ -198,14 +216,15 @@ public:
 
         glEnable(GL_TEXTURE_2D);
         glBindTexture(GL_TEXTURE_2D, m_texid);
-        glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, m_size.x, m_size.y,
+        glTexSubImage2D(GL_TEXTURE_2D, 0,
+                        0, m_frame * m_size.y / 2, m_size.x / 2, m_size.y / 2,
 #if !defined __CELLOS_LV2__
                         GL_RGBA, GL_UNSIGNED_BYTE,
 #else
                         /* The PS3 is big-endian */
                         GL_RGBA, GL_UNSIGNED_INT_8_8_8_8,
 #endif
-                        m_pixels);
+                        m_pixels + m_size.x * m_size.y / 4 * m_frame);
 
         m_shader->Bind();
 #if !defined __CELLOS_LV2__ && !defined __ANDROID__ && !defined __APPLE__
@@ -257,7 +276,7 @@ private:
     bool m_ready;
 
     f64cmplx m_center, m_target;
-    double m_radius;
+    double m_radius, m_angle;
 };
 
 int main()
@@ -270,6 +289,7 @@ int main()
 
     new DebugFps(5, 5);
     new Fractal(ivec2(640, 480));
+    //new DebugRecord("fractalol.ogm", 60.0f);
 
     app.Run();