I'm calling glDrawArrays twice, the first time i see the drawing and the second time nothing is drawn.
static GLfloat vVertices[] = {
-1.0f, 1.0f, 0.0f,
-1.0f, -1.0f, 0.0f,
1.0f, -1.0f, 0.0f,
1.0f, 1.0f, 0.0f,
-1.0f, 1.0f, 0.0f,
/* diagonal lines */
/*from left bottom to right up */
-1.0f, -1.0f, 0.0f,
1.0f, 1.0f, 0.0f,
/* from left up to right bottom */
-1.0f, 1.0f, 0.0f,
1.0f, -1.0f, 0.0f,
};
glEnableVertexAttribArray( attribPosition);
glVertexAttribPointer( attribPosition, 3, GL_FLOAT, GL_TRUE, 0, vVertices);
glDrawArrays ( GL_LINE_STRIP, 0, 5 );
glDrawArrays ( GL_LINES, 15, 2 ); // this is not drawn
i'm sure that i draw right, because i see the first call drawingm, but what is the problem with the second?
thanks
I understood my problem.
The second argument is the vertex index, and not the index in the array itself, so the last line should be:
glDrawArrays( GL_LINES, 5, 2);
Related
I am using OPEN GL ES2.0 on Android.
I need pass two attributes to shader, one for position, one for texture coordinates,
//vertices for position
vertices = new float[12] { -1.0f, -1.0f, 1.0f, -1.0f, 1.0f, 1.0f, -1.0f,
-1.0f, 1.0f, 1.0f, -1.0f, 1.0f };
//vertices for texture coordinates.
txtVertices = new float[12] { 0.0f, 0.0f, 1.0f, 0.0f, 1.0f, 1.0f, 0.0f,
0.0f, 1.0f, 1.0f, 0.0f, 1.0f };
//Passing to shader.
glVertexAttribPointer(texCoordHandle, 2, GL_FLOAT, GL_FALSE, 0,
txtVertices);
glVertexAttribPointer(vPositionHandle, 2, GL_FLOAT, GL_FALSE, 0, vertices);
glEnableVertexAttribArray(vPositionHandle);
glEnableVertexAttribArray(texCoordHandle);
glDrawArrays(GL_TRIANGLES, 0, 6);
glDisableVertexAttribArray(vPositionHandle);
glDisableVertexAttribArray(texCoordHandle);
What's the problem of this piece of code? it's like the second one override the first one, and only one vertices are passed into my shader.
it seems that ther is no error in the code you posted. may have errors in shaders or in some other part
don't you pass 3 floats for vertexposition(x,y,z)
I need to draw a 10 x 10 grid in OpenGL ES 2.0. Are triangle strips the best way to do this? How do you draw this without drawing the diagonal lines? All of the searches that I come up with show grid lines with the diagonals drawn, but this defeats the purpose.
I've drawn the grid just using a bunch of lines, but I'm having trouble transforming it as a unit. Is this the right approach, but I'm not executing it correctly? Or is there a better way, like triangle strips? Thanks!
// draw the horizontal gridlines
for (i=0; i<12; i++) {
modelViewMatrixRight = GLKMatrix4MakeTranslation(0.0f, 1.0f/11.0f*(float)i - 0.5f, -2.0f);
// modelViewMatrixRight = GLKMatrix4Rotate(modelViewMatrixRight, GLKMathDegreesToRadians(-45.0f), 0.0f, 0.0f, 1.0f);
_modelViewProjectionMatrix = GLKMatrix4Multiply(projectionMatrixRight, modelViewMatrixRight);
glUniformMatrix4fv(uniforms[UNIFORM_MODELVIEWPROJECTION_MATRIX], 1, 0, _modelViewProjectionMatrix.m);
glUniformMatrix3fv(uniforms[UNIFORM_NORMAL_MATRIX], 1, 0, _normalMatrix.m);
glUniform4fv(uniforms[UNIFORM_COLOR_VECTOR], 1, _color);
glBindVertexArrayOES( [my_line[i] getVertexArray] ); // make this line the current object
[my_line[i] render];
}
// draw the vertical gridlines
for (i=12; i<24; i++) {
modelViewMatrixRight = GLKMatrix4MakeTranslation(0.5f - 1.0f/11.0f * (float) (i-12), 0.0f, -2.0f);
modelViewMatrixRight = GLKMatrix4Rotate(modelViewMatrixRight, GLKMathDegreesToRadians(90.0f), 0.0f, 0.0f, 1.0f);
modelViewMatrixRight = GLKMatrix4Rotate(modelViewMatrixRight, GLKMathDegreesToRadians(60.0f), 1.0f, 0.0f, 1.0f);
_modelViewProjectionMatrix = GLKMatrix4Multiply(projectionMatrixRight, modelViewMatrixRight);
glUniformMatrix4fv(uniforms[UNIFORM_MODELVIEWPROJECTION_MATRIX], 1, 0, _modelViewProjectionMatrix.m);
glUniformMatrix3fv(uniforms[UNIFORM_NORMAL_MATRIX], 1, 0, _normalMatrix.m);
glUniform4fv(uniforms[UNIFORM_COLOR_VECTOR], 1, _color);
glBindVertexArrayOES( [my_line[i] getVertexArray] ); // make this line the current object
[my_line[i] render];
}
I want to draw cubes using textures.
void OperateWithMainMatrix(ESContext* esContext, GLfloat offsetX, GLfloat offsetY, GLfloat offsetZ) {
UserData *userData = (UserData*) esContext->userData;
ESMatrix modelview;
ESMatrix perspective;
//Manipulation with matrix
...
glVertexAttribPointer(userData->positionLoc, 3, GL_FLOAT, GL_FALSE, 0, cubeFaces);
//in cubeFaces coordinates verticles cube
glVertexAttribPointer(userData->normalLoc, 3, GL_FLOAT, GL_FALSE, 0, cubeFaces);
//for normals (use in fragment shaider for textures)
glEnableVertexAttribArray(userData->positionLoc);
glEnableVertexAttribArray(userData->normalLoc);
// Load the MVP matrix
glUniformMatrix4fv(userData->mvpLoc, 1, GL_FALSE,
(GLfloat*)&userData->mvpMatrix.m[0][0]);
//Bind base map
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_CUBE_MAP, userData->baseMapTexId);
//Set the base map sampler to texture unit to 0
glUniform1i(userData->baseMapLoc, 0);
// Draw the cube
glDrawArrays(GL_TRIANGLES, 0, 36);
}
(coordinates transformation is in OperateWithMainMatrix() )
Then Draw() function is called:
void Draw(ESContext *esContext)
{
UserData *userData = esContext->userData;
// Set the viewport
glViewport(0, 0, esContext->width, esContext->height);
// Clear the color buffer
glClear(GL_COLOR_BUFFER_BIT);
// Use the program object
glUseProgram(userData->programObject);
OperateWithMainMatrix(esContext, 0.0f, 0.0f, 0.0f);
eglSwapBuffers(esContext->eglDisplay, esContext->eglSurface);
}
This work fine, but if I try to draw multiple cubes (next code for example):
void Draw(ESContext *esContext)
{ ...
// Use the program object
glUseProgram(userData->programObject);
OperateWithMainMatrix(esContext, 2.0f, 0.0f, 0.0f);
OperateWithMainMatrix(esContext, 1.0f, 0.0f, 0.0f);
OperateWithMainMatrix(esContext, 0.0f, 0.0f, 0.0f);
OperateWithMainMatrix(esContext, -1.0f, 0.0f, 0.0f);
OperateWithMainMatrix(esContext, -2.0f, 0.0f, 0.0f);
eglSwapBuffers(esContext->eglDisplay, esContext->eglSurface);
}
A side faces overlapes frontal face. This process is illustrated on image:
Alternate picture (with colours and clean image):
The side face of the right cube overlaps frontal face of the center cube.
How can i remove this effect and display miltiple cubes without it?
To fix this you need to utilize what's known as the depth buffer. This is what's responsible for making sure that surfaces don't get drawn overtop of surfaces that are nearer (like the side of a cube showing over the front of a cube).
Luckily it's not much work involved to do so:
Enable depth testing at initialization with glEnable(GL_DEPTH_TEST)
Clear depth buffer on each frame by adding it's bit to the glClear call:
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT)
After this you should no longer see your surfaces popping on top of nearer surfaces.
I'm writing an iOS game that draws many cubes on screen, but I have a problem with positioning the cubes.
I have a function draw_voxel that draws a cube:
void draw_voxel(Point location, Color color, GLKMatrixStackRef stack) {
GLKMatrixStackPush(stack);
GLKMatrixStackTranslate(stack, location.x, location.y, location.z);
std::array<Color, 36> triangle_colors;
triangle_colors.fill(color);
glEnableVertexAttribArray(GLKVertexAttribPosition);
glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, 0, static_cast<const GLvoid*>(triangle_vertices.data()));
glEnableVertexAttribArray(GLKVertexAttribColor);
glVertexAttribPointer(GLKVertexAttribColor, 4, GL_FLOAT, GL_FALSE, 0, static_cast<const GLvoid*>(triangle_colors.data()));
glDrawArrays(GL_TRIANGLES, 0, 36);
glDisableVertexAttribArray(GLKVertexAttribPosition);
glDisableVertexAttribArray(GLKVertexAttribColor);
GLKMatrixStackPop(stack);
}
I pass it a GLKMatrixStackRef, push the current matrix on top and use GLKMatrixStackTranslate to translate the top matrix. However, all cubes are still drawn at (0, 0, 0).
I call draw_voxel like this:
[self.effect prepareToDraw];
GLKMatrixStackRef stack = GLKMatrixStackCreate(nullptr);
draw_voxel(Point(-1.0f, 0.0f, 0.0f), Color(1.0f, 0.0f, 0.0f, 1.0f), stack);
draw_voxel(Point(+0.0f, 0.0f, 0.0f), Color(0.0f, 1.0f, 0.0f, 1.0f), stack);
draw_voxel(Point(+1.0f, 0.0f, 0.0f), Color(0.0f, 0.0f, 1.0f, 1.0f), stack);
CFRelease(stack);
I couldn't find any useful information on the internet about GLKit matrix stacks, and I'm really stuck. How do I "apply" the top matrix so that the cubes are translated?
While I still haven't fully grasp how to use GLKMatrixStack, looking at your code I think the problem is that you are not passing the top matrix of the stack to the shader, or, in GLKit words, you are not properly configuring the effect.
Probably, at some point you should be doing something like:
self.effect.transform.modelviewMatrix = GLKMatrixStackGetMatrix4(stack);
Hope this help, I'm stuck on that stack too :)
I have the following vertex shader:
attribute vec4 Position;
attribute vec4 SourceColor;
varying vec4 DestinationColor;
uniform mat4 Projection;
void main(void) {
DestinationColor = SourceColor;
gl_Position = Projection * Position;
}
I then try to apply the following matrix to the Projection uniform:
float matrix[16] = {
1.0f, 0.0f, 0.0f, 0.0f,
0.0f, 1.0f, 0.0f, 0.0f,
0.0f, 0.0f, 1.0f, 0.0f,
0.0f, 0.0f, 0.0f, 1.0f
};
glUniformMatrix4fv(projectionSlot, 1, GL_FALSE, matrix);
Shouldn't this do nothing? After running this, I can't see my objects on the screen anymore...
Yes it should be a no-op. If you remove the projection multiply then you say it works fine?
Couple ideas:
Check glGetError
Check shader compile/link status (glGetShader/Programiv)
Is the program bound during glUniform call?
Is projectionSlot a valid value?
I've never used matrices in programming, but I've taken lot's of math courses. Don't know how the Projection you're using works, but keep in mind the projection of x onto y is very different than projection of y onto x. Try switching them around if you haven't.