Hi Im having trouble with glselection using ortho projection. I am developing a tile based engine. The code below renders a map 64 x 64. each tile is 32 x 32 pixals.
With this code I am able to correctly get the x coordinate for the tile in the map, but the y coordinate is messed up.
Im gonna try to explain it. the y axis for the mouse runs from top to bottom. 0 - 480.
the selection code interprets the mouse position as this.
0 10
1 9
2 8
3 7
4 6
5 5
6 4
7 3
8 2
9 1
10 0
anyway here is the code I am using…
void SelectObject(void)
{
int x,
y;
GLfloat tempx,
tempy;
//initialize name stack
glInitNames();
glPushName(0);
glDisable(GL_TEXTURE_2D);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
//draw names map
for(y = 0 ; y < 65 ; y++)
{
for(x = 0 ; x < 65 ; x++)
{
tempx = x + camera.x;
tempy = y + camera.y;
//only draws viewable tiles
if((tempx >= -1) && (tempx <= 20) && (tempy >= -1) && (tempy <= 20))
{
//stores name as x.y
glLoadName(x * 100 + y);
glBegin(GL_QUADS);
glVertex3d(tempx * 32 , tempy * 32, 0); //Top Left
glVertex3d(tempx * 32 + 32, tempy * 32, 0); //Top Right
glVertex3d(tempx * 32 + 32, tempy * 32 + 32, 0); //Bottom Right
glVertex3d(tempx * 32 , tempy * 32 + 32, 0); //Bottom Left
glEnd();
}
}
}
}
#define BUFFER_LENGTH 64
void ProcessSelection(int xPos, int yPos)
{
float temp,
tempy;
// Space for selection buffer
GLuint selectBuff[BUFFER_LENGTH];
// Hit counter and viewport storage
GLint hits, viewport[4];
// Set up selection buffer
glSelectBuffer(BUFFER_LENGTH, selectBuff);
// Get the viewport
glGetIntegerv(GL_VIEWPORT, viewport);
// Switch to projection and save the matrix
glMatrixMode(GL_PROJECTION);
glPushMatrix();
// Change render mode
glRenderMode(GL_SELECT);
// Establish new clipping volume to be unit cube around
// mouse cursor point (xPos, yPos) and extending two pixels
// in the vertical and horizontal direction
glLoadIdentity();
gluPickMatrix(xPos, yPos, 2,2, viewport);
// Apply perspective matrix
glOrtho(0.0f,640,480,0.0f,-1.0f,1.0f);
// Draw the scene
SelectObject();
// Collect the hits
hits = glRenderMode(GL_RENDER);
// If a single hit occurred, display the info.
if(hits == 1)
{
temp = float(selectBuff[3]);
tileid.x = int(floor(temp / 100));
tempy = ((temp / 100) - tileid.x) * 100;
tileid.y = int(tempy);
}
// Restore the projection matrix
glMatrixMode(GL_PROJECTION);
// Go back to modelview for normal rendering
glMatrixMode(GL_MODELVIEW);
// Restore the matrix state
glPopMatrix(); // Modelview matrix
}