The Matrix Stack functionality is deprecated and I want to draw multiple objects with different transformations.
I imagine I can accomplish different object transformations by manually sending in a matrix via a uniform to a shader. Here is what I have now:
glUseProgram(shaderProgram);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
GLint posAttrib = glGetAttribLocation(shaderProgram, "vertexPosition");
glEnableVertexAttribArray(posAttrib);
GLint colorAttrib = glGetAttribLocation(shaderProgram, "vertexColor");
glEnableVertexAttribArray(colorAttrib);
GLfloat ortho = glGetUniformLocation(shaderProgram, "projection");
float r = 1.875;
float l = -1.875;
float b = -1.5;
float t = 1.5;
float n = 0;
float f = 5;
float orthoElements[] =
{
2 / (r - l), 0, 0, -(r + l) / (r - l),
0, 2 / (t - b), 0, -(t + b) / (t - b),
0, 0, -2 / (f - n), (f + n) / (f - n),
0, 0, 0, 1,
};
glUniformMatrix4fv(ortho, 1, GL_TRUE, orthoElements);
//Draw AXES
glVertexAttribPointer(posAttrib, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)(sizeof(vertices) + sizeof(colors) + sizeof(edgeColors)));
glVertexAttribPointer(colorAttrib, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(float), (void*)(sizeof(vertices) + sizeof(colors) + sizeof(edgeColors) + 3 * sizeof(float)));
glDrawArrays(GL_LINES, 0, sizeof(axes) / (6 * sizeof(axes[0])));
GLfloat rot = glGetUniformLocation(shaderProgram, "rotation_y");
float angle = -45 + persp;
//rotates "angle" degrees about the y-axis
float rotElements[] =
{
cosf(angle), 0, sinf(angle), 0,
0, 1, 0, 0,
-sinf(angle), 0, cosf(angle), 0,
0, 0, 0, 1,
};
glUniformMatrix4fv(rot, 1, GL_TRUE, rotElements);
//draw other stuff
To sum up the code above, I first apply orthographic projection to the whole scene, then I draw the coordinate axes. After that I apply an extra rotation about the y-axis and then draw extra stuff. Because I have axes’ draw calls after the projection transformation and before the rotation transformation, I expect the axes be affected only by the projection transformation. But it seems that all transformations whose matrices I send to the shader accumulate and affect everything, be it above or below the transformation code.
Why is that happening? And how can I “protect” my draw calls from transformations below affecting them? In other words, I want to have control over which objects are affected by which transformations.