In my app, I draw a series of points (stars) and then a series of lines (constellation figures) but the lines are flickering on the simulator and when I run the app on my iPhone there are no lines at all. Any ideas?
(I'm running OpenGL 2.0 ES in a GLKView under a GLKViewController.)
Edit: Here is the drawing code where I use a custom shader for the stars but I don't really need it for the lines. Not sure how to return to a default shader. (I've tried glUseProgram(0); which is supposed to work but it makes no difference.)
- (void)drawRect:(CGRect)rect {
// Drawing code
// NSLog(@"GBStarField drawRect invoked!");
/*********************************/
// Draw all stars
/*********************************/
// Clear the framebuffer
glClearColor(0.0, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
// Calculate OpenGL to GLKit View coordinate transformation
// Calculate perspective transformation
float aspect = fabsf(self.bounds.size.width / self.bounds.size.height);
GLKMatrix4 projectionMatrix = GLKMatrix4MakePerspective(GLKMathDegreesToRadians(90.0f), aspect, 0.0f, 10.0f);
self.effect.transform.projectionMatrix = projectionMatrix;
// Calculate translation transformation
#ifdef USE_RA_DEC
GLKMatrix4 modelViewMatrix = GLKMatrix4MakeTranslation(0.0f, 0.0f, 0.0f);
#else
GLKMatrix4 modelViewMatrix = GLKMatrix4MakeTranslation(0.0f, 0.0f, -2.0f);
#endif
// Calculate rotation transformation
// remember the right hand rule for rotation vector
modelViewMatrix = GLKMatrix4Rotate(modelViewMatrix, GLKMathDegreesToRadians(rotation/10), 0, 1, 0);
//modelViewMatrix = GLKMatrix4Rotate(modelViewMatrix, GLKMathDegreesToRadians(-90), 0, 0, 1); // polaris
//modelViewMatrix = GLKMatrix4Rotate(modelViewMatrix, GLKMathDegreesToRadians(180-279.2346), 0, 1, 0); // vega
//modelViewMatrix = GLKMatrix4Rotate(modelViewMatrix, GLKMathDegreesToRadians(-38.783692), 0, 0, 1); // vega
//modelViewMatrix = GLKMatrix4Rotate(modelViewMatrix, GLKMathDegreesToRadians(180-78.63447), 0, 1, 0); // rigel
//modelViewMatrix = GLKMatrix4Rotate(modelViewMatrix, GLKMathDegreesToRadians(8.20164), 0, 0, 1); // rigel
self.effect.transform.modelviewMatrix = modelViewMatrix;
[self.effect prepareToDraw];
// Get uniform locations (must be after linking)
GLint u_projectionMatrixLocation;
u_projectionMatrixLocation = glGetUniformLocation(programBrightStar, (const GLchar*) "u_projectionMatrix");
GLint u_modelViewMatrixLocation;
u_modelViewMatrixLocation = glGetUniformLocation(programBrightStar, (const GLchar*) "u_modelViewMatrix");
// Get attribute locations (must be after linking)
GLint a_positionLocation;
a_positionLocation = glGetAttribLocation(programBrightStar, (const GLchar*) "a_position");
GLint a_colorLocation;
a_colorLocation = glGetAttribLocation(programBrightStar, (const GLchar*) "a_color");
GLint a_pointsizeLocation;
a_pointsizeLocation = glGetAttribLocation(programBrightStar, (const GLchar*) "a_pointsize");
// Working with the star buffers
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer);
glGetBufferParameteriv(GL_ARRAY_BUFFER, GL_BUFFER_SIZE, &vertexBufferSize);
//NSLog(@"vertexBufferSize/sizeof(Vertex) = %lu", vertexBufferSize/sizeof(Vertex));
// Use custom vertex/fragment shader (must be after binging the buffers
glUseProgram(programBrightStar);
// Set uniforms for shader (must be after "glUseProgram")
glUniformMatrix4fv(u_projectionMatrixLocation, 1, GL_FALSE, projectionMatrix.m);
glUniformMatrix4fv(u_modelViewMatrixLocation, 1, GL_FALSE, modelViewMatrix.m);
// Set attributes for shader (must be after "glUseProgram")
glEnableVertexAttribArray(a_positionLocation);
glVertexAttribPointer(a_positionLocation, 4, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid *) offsetof(Vertex, Position));
glEnableVertexAttribArray(a_colorLocation);
glVertexAttribPointer(a_colorLocation, 4, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid *) offsetof(Vertex, Color));
glEnableVertexAttribArray(a_pointsizeLocation);
glVertexAttribPointer(a_pointsizeLocation, 1, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid *) offsetof(Vertex, Pointsize));
// Draw it as points defined by the vertex and index buffer data
glDrawArrays(GL_POINTS, 0, vertexBufferSize/sizeof(Vertex));
/*********************************/
// Draw all constellations
/*********************************/
// Working with the constellation buffers
glBindBuffer(GL_ARRAY_BUFFER, constellationVertexBuffer[0]);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, constellationIndexBuffer[0]);
glGetBufferParameteriv(GL_ELEMENT_ARRAY_BUFFER, GL_BUFFER_SIZE, &indexBufferSize);
//NSLog(@"indexBufferSize/sizeof(GLuint) = %lu", indexBufferSize/sizeof(GLuint));
// Use custom vertex/fragment shader (must be after binging the buffers
glUseProgram(programBrightStar);
// Set uniforms for shader (must be after "glUseProgram")
glUniformMatrix4fv(u_projectionMatrixLocation, 1, GL_FALSE, projectionMatrix.m);
glUniformMatrix4fv(u_modelViewMatrixLocation, 1, GL_FALSE, modelViewMatrix.m);
// Set attributes for shader (must be after "glUseProgram")
glEnableVertexAttribArray(a_positionLocation);
glVertexAttribPointer(a_positionLocation, 4, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid *) offsetof(Vertex, Position));
glEnableVertexAttribArray(a_colorLocation);
glVertexAttribPointer(a_colorLocation, 4, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid *) offsetof(Vertex, Color));
glEnableVertexAttribArray(a_pointsizeLocation);
glVertexAttribPointer(a_pointsizeLocation, 1, GL_FLOAT, GL_FALSE, sizeof(Vertex), (const GLvoid *) offsetof(Vertex, Pointsize));
// Draw it as lines defined by the vertex and index buffer data
glDrawElements(GL_LINES, indexBufferSize/sizeof(GLuint), GL_UNSIGNED_INT, 0);
}
I found the problem. It was my shader. I had a shader for stars that made circles from large square points. This was rejecting the lines as the image was rotated. I solved the problem by adding a second shader to draw the lines.