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Why does the minus operator give different result than the TIMESTAMPDIFF() function in mysql?

- by f3r3nc

Since TIMESTAMP in mysql is stored as a 32bit value representing the time interval from 1970-jan-1 0:00:00 in seconds, I assumed that using minus (-) operator on TIMESTAMP values would give the difference of these values in seconds. Actually not: +---------------------------------------------------------------------+ | TIMESTAMP("2010-04-02 10:30:00") - TIMESTAMP("2010-04-02 10:29:59") | +---------------------------------------------------------------------+ | 41.000000 | +---------------------------------------------------------------------+ 1 row in set (0.05 sec) mysql> select timestampdiff(SECOND,TIMESTAMP("2010-04-02 10:30:00"),TIMESTAMP("2010-04-02 10:29:59")); +-----------------------------------------------------------------------------------------+ | timestampdiff(SECOND,TIMESTAMP("2010-04-02 10:30:00"),TIMESTAMP("2010-04-02 10:29:59")) | +-----------------------------------------------------------------------------------------+ | -1 | +-----------------------------------------------------------------------------------------+ mysql> select TIMESTAMP("2010-04-02 10:30:00") - TIMESTAMP("2010-04-02 10:30:01") ; +---------------------------------------------------------------------+ | TIMESTAMP("2010-04-02 10:30:00") - TIMESTAMP("2010-04-02 10:30:01") | +---------------------------------------------------------------------+ | -1.000000 | +---------------------------------------------------------------------+ +---------------------------------------------------------------------+ | TIMESTAMP("2010-04-02 10:30:00") - TIMESTAMP("2010-04-02 10:31:00") | +---------------------------------------------------------------------+ | -100.000000 | +---------------------------------------------------------------------+ It seems like one minute difference is 100 instead of 60. Why is this?

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Why is this OpenGL ES code slow on iPhone?

- by f3r3nc

I've slightly modified the iPhone SDK's GLSprite example while learning OpenGL ES and it turns out to be quite slow. Even in the simulator (on the hw worst) so I must be doing something wrong since it's only 400 textured triangles. const GLfloat spriteVertices[] = { 0.0f, 0.0f, 100.0f, 0.0f, 0.0f, 100.0f, 100.0f, 100.0f }; const GLshort spriteTexcoords[] = { 0,0, 1,0, 0,1, 1,1 }; - (void)setupView { glViewport(0, 0, backingWidth, backingHeight); glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrthof(0.0f, backingWidth, backingHeight,0.0f, -10.0f, 10.0f); glMatrixMode(GL_MODELVIEW); glClearColor(0.3f, 0.0f, 0.0f, 1.0f); glVertexPointer(2, GL_FLOAT, 0, spriteVertices); glEnableClientState(GL_VERTEX_ARRAY); glTexCoordPointer(2, GL_SHORT, 0, spriteTexcoords); glEnableClientState(GL_TEXTURE_COORD_ARRAY); // sprite data is preloaded. 512x512 rgba8888 glGenTextures(1, &spriteTexture); glBindTexture(GL_TEXTURE_2D, spriteTexture); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, spriteData); free(spriteData); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR); glEnable(GL_TEXTURE_2D); glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA); glEnable(GL_BLEND); } - (void)drawView { .. glClear(GL_COLOR_BUFFER_BIT); glLoadIdentity(); glTranslatef(tx-100, ty-100,10); for (int i=0; i<200; i++) { glTranslatef(1, 1, 0); glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); } .. } drawView is called every time the screen is touched or the finger on the screen is moved and tx,ty are set to the x,y coordinates where that touch happened. I've also tried using GLBuffer, when translation was pre-generated and there was only one DrawArray but gave the same performance (~4 FPS). ===EDIT=== Meanwhile I've modified this so that much smaller quads are used (sized: 34x20) and much less overlapping is done. There are ~400 quads-800 triangles spread on the whole screen. Texture size is 512x512 atlas and RGBA_8888 while the texture coordinates are in float. The code is very ugly in terms of API efficiency: there are two MatrixMode change along with two loads and two translation then a drawarrays for a triangle strip (quad). Now this produces ~45 FPS.